Need answers

Hey everyone,
This is probably going to be quite long not sure why im writing in maybe i just need to vent and for someone to tell me everything is ok or atleast will be.
It all starts with my mother and my childhood. I feel as though i have been put through alot and have had to be responsible for such things that no child should have to deal with. I feel as though i was forced to 'grow up' at an early age and its put alot of pressure on me even as an adult i am now 23. Anyways my mother has always been a very selfish, reckless and irresponsible person always putting her needs before others and playing the victim and acting as though the world owes her everything. She is not a very stable person and she has always lived her life around her needs rather than what is best for her children. When i was 12 my uncle passed away and at the time i was living with my nan, i had a younger sister who was still only about 3. I knew my mother was struggling especially being a single mother and her best friend had just passed away so i made the decision to move back. She struggled with an alcohol and drug addiction and i was the only support person she really had i practically helped her raise my sister always having to babysit and being left home alone with her while she was out drinking or scoring drugs. She was very abusive towards us when she was coming down off the drugs or had none or she would be hungover from the constant drinking. I felt as though i was trapped and i had no other family where we were my father wasnt in the picture at the time and neither was my sisters father. I really stuggled as an early teen dealing with all this i had so much put onto my shoulders at such a delicate age where i should have had the most support but in turn was supporting my mother. We eventually left that town and moved back to our home town and my other little sister was born. When she was only a baby and i was 16 i met a boy and him and his family took me in. I could not handle my mother any longer and i left. Before i get people asking me why i never reached out to anyone for help well i was scared. As much as i hated my mother i also love her just as much and i couldnt bare the thought of losing her all together or having me and my sisters taken away. I mean as far as i knew she had given away the drugs, still drank occasionally but i fear she still suffered depression and all sorts. My middle sister was bounced back and forth from my mother and her father for years they had shared custody as he finally decided he would have something to do with her. Fast forward to now she is 15 and now living with me because her father has completely wiped her from his life and my mother and her fight like cats and dogs. My sister is quite depressed and suffers from anxiety also (ive got her medicated for it, doctors orders) she has been to counselling in the past but that didnt really help her. But the reason im writing this is because im really struggling with all of this. I also have anxiety and had been taking medication for it the last 2 years but as i am 21 weeks pregnant i had to stop cold turkey. I have a full on 3 year old son. I do have a partner and he helps when he can but i now have the responsibility of a 15 year old girl. Who is hugely emotion and also very overweight and all she wants to do is sit around and eat food. Shes depressed i guess it happens. But all think about is how much i resent my mother and her father because here they are living it up enjoying themselves not a worry while im here doing all of their responsibilities for them because they are both such poor excuses for parents. I feel like every poor decision my mother has ever made has always affected my life. I have tried my hardest to make the best life for myself and my family away from her and her problems but i can never seem to escape it. Its just not fair and i feel like im drowning in sorrow. Considering everything i went through growing up i think ive done pretty well with myself. Besides the dreams i have every now and then that is a constant reminder of the childhood i endured and the anxiety and most likely depression. I have seen a psychologist but she didn't want to discuss my past only the present and i feel like the past is the root to all my mental issues. I would love to be able to get past the resentment towards my mother as it only causes me pain but she cannot be reasoned with at all and frankly she doesnt give to shits about me or my sister i tried to explain the struggle im having with the responsibility and all she said is not my problem now. I feel like she is ruining my life and has been from the beginning and i cant get away. I just want to scream at her and tell her how much i hate her for everything she has done to me. I have tried to explain how i feel and tell her that some things she has done has really messed with my head but she refuses to believe she has ever done anything wrong. When will this nightmare end. I know im doing a good thing for me sister i just dont feel like it should be my responsibility im trying to live my own life. And i feel like i did enough helping our mother raise her as a child. I guess i just need someone to tell me i am doing the right thing and that im a strong person for doing this. Because i cant help but second guess myself for taking on such a responsibility. ?

Also i should add:
She is constantly trying to get out of going to school she is in year 9 and she needs to go. Numerous times she has rang me or texted me saying she wants to come home because none of her friends are there and she is alone and i keep having to remind her that she goes to school to learn and not to socialise. She had so much time off this year while she was still at our mothers as in weeks worth. She always says shes 'sick' or if she knows im in a mood but too afraid to ask to stay home she will mope around and once at school will go to sick bay and then i have to go get her otherwise i look bad. She also has a job that was basically given to her that she has had since feb but always complains that she has to work. She told me yesterday that her boss asked her to work today and that she said no (she wants me to help her find another job) and when i told her that if she keeps letting her boss down she wont get any shifts she replied with its ok im getting a new job anyway. Today i had a go at her because she lied to me she didnt turn her boss down at all she said she would work cause she felt bad and now she turned around an told her boss she was sick and couldnt come in. (Apparently she has a headache and is getting her period) i dont find this a legitimate excuse at all. It is just pure laziness. I dont feel i should help her find a new job as she is showing no initiative for her current job and is just taking it for granted i cant see it changing with anything else. Whenever i call her out on such things she plays the whole reverse psychology/ guilt trip/ im innocent card and acts like she has no idea what im talking about. She will also bring things up about me to try justify her actions. Im an adult she is a child who is under my care how do i make her understand this. I feel as though she is being disrespectful towards me by not keeping up with her responsibilities she is old enough to know right from wrong and im not having her slack off. But everytime i try talk to her about things she plays the victim and starts crying and im getting no where with her. Im so tired of it.