How do you get over being everything you never wanted to be?

Ever since I was a little girl I've always known I wanted kids but never be a full time stay at home mum. I've always needed to be busy and thrive off working and pressure. My first child I went back to work weekends that was fine. After that her dad and I split and when I re-partnered and had more children circumstances changed and me working wasn't an option due to partners work and no family/friend support so I've now been a stay at home mum for 5 years. Don't get me wrong I love my kids whole heartedly but I hate being home all the time. I need to feel challenged and independent and use my brain for more then cleaning,cooking and playing. I am studying so i can change career so its an option for me to work but in the meantime how the hell are you meant to accept being everything you never wanted to be? I've been trying to do this for 5 years. But its just not enough. I knoe this post will likely attract the haters and I honestly dont care. I just need others opinions on how to deal with this so I can stop feeling resentment and so much anger. Its affecting my marriage and I'm finding myself more and more angry about it and I need to fix it but at a complete loss.