My mom keeps forcing me to eat?

Ok so i'm starr. I'm 13, 5'3, 118lbs. I really want to lose weight, but my mom keeps making things i have to eat or she will start getting all weird like she did about a month ago when i refused dinner a few nights. I currently play two sports (soccer and lacrosse) and after my practice this weekend she took me out for donuts, and i couldn't turn them down or she'll kirk out on me. This whole week it has been SUGAR FAT CARBS SUGAR AND MORE CARBS!!! She just won't let me eat my 300 calories a day in fruit and vegetables. I know she is trying to keep me healthy, but this is making everything worse! My sisters are overweight and i weigh the least in my house(less than my 10 year old sister) so when i start caring about what i put down my throat something must be wrong! Also i have come a lot closer to purging this week than i ever have before. I have recently started making sure i drink all most a cup of water in between bites, which i have to chew 20 times unless it's meat, in which case it must be chewed 30 times. I don't like it when people see me eat anymore and i have stopped drinking milk. Does anybody have any idea how to make her stop? Or if i can't get her to stop, at least make her shove healthy stuff down my throat!?