What do I do to become a better mum?

I am really struggling with being a mum at the moment. I feel I am under an incredible amount of stress. I get like this on and off, I have been diagnosed with several mental health conditions and haven't been medicated for almost 4 years. Looking back all the medication did was just mask emotions and feelings. I still had moments where I felt overwhelmed. I am a single mother of 2 children, im halfway through a university degree, I raise my children completely alone with no help from family nor friends, minimal support also. Lately I have been so on edge, not sleeping well at all, not eating much as I have a very small appetite, however some nights I binge on chocolate. I can not stand the way I have become towards my children, admittedly they have been walking all over me and the minute I try to take control of a situation they whinge and complain and make me feel awful. They are loved and well looked after, always food in the cupboards and I take them out to do fun things and keep them busy and stimulated, yet when they don't listen I fear I am emulating my mother's behaviours as I was growing up. She would be emotionally and physically abusive, she would lose it at the flick of a switch. The only difference between me and her is that I'm not physically abusing my children and that is one thing I swore I would never do when I became a parent, I also swore to myself I would never be anything like her yet here I am getting so angry and frustrated with my children. It upsets me at the end of a long day, the guilt eats away at me and I feel the depression get worse. I have tried so hard to change things and change the way I am. Tried to make things more positive for example say to them if you can help clean up your toys we can sit down together and watch a movie and just spend time together. I don't know what else to do. I have tried speaking with my doctor about my feelings about the way I've become and he puts it down to stress. I know I need a break so I can take time out for me and reassess the way things are and have the mindset to take a different approach to things but that just isn't possible. Father not involved in children's lives, family won't assist me to get that break I need and I'm at a loss what to do. Is there any positive feedback or suggestions other mums could give me please. Please don't make me feel worse than I already do I really need positive and supportive comments please 😔