Cara...do not quit your meds, there can be serious effects just stopping certain medicines, sometimes it needs to be done slowly.
Do you have a friend who can take you? How about your sister? Talk to your Mom, tell her you really think you need to go (even though I'm guessing you think you don't). Therapy does help and it's important to go.
About your weight, some meds will cause you to store more water and/or fat. I'm guessing these meds are really helping you, so again, do not just stop taking them. Ignore the weight comments, I've seen pics of you and you are not fat. I know every teenage girl thinks they are fat when they aren't!
My Mother had some very serious illnesses and was in pain all the time. Her doctor gave her some anti-depressents to help her through it, and she felt great. She felt so much better that she thought she didn't need them anymore so she stopped taking them, she crashed bigtime....she was even more depressed than before. Do not stop your meds without talking to your doctor.
Sending good wishes your way...hang in there! In a couple years you will be able to move out and be on your own, so use this time to get yourself "right and ready". Concentrate on you (which includes doing better in school, so I hope that's getting better)!