Learn to say no. You are only human you can't do everything for everyone. I know, I've been there. Depending on the people your dealing with I'm sure they will understand, and if they don't it's not your fault. It's all about how you think about it. When I was a people pleaser, I thought people would be mad at me for saying no. When I said no I was so relieved when I saw how okay they were with my answer and if they don't understand oh well. You don't have to give them an explanation but you can if you want to.
Besides you are still very young you can turn your life around. Go back to school and pursue your dreams despite what people think or say.I once read "what people say about you isn't any of your business."
I also suggest you try to spend at least one day a week spending time with yourself. Take a break from the world and relax to show yourself you really care