Roommate problems...Help!

Since I've moved out of my parent's house to go to college, I have been staying on campus in the dorms. Yes, I have a roommate. Don't even get me started on how hard it is to live with someone you had never met before it was time to move in together. Needless to say, we have our struggles. But I have grown to like her for the most part and call her a friend.

The one thing that bothers me most about her is how overbearing she is. Mostly about my weight/eating habits/exercise. I have never been a person who likes confrontation. If someone is mean to me or tries to boss me around or does bad things to me, I just take it. I don't know why. I hate myself for letting people walk all over me. But I just can't stick up for myself. I've never been able to. I would just rather avoid the entire situation and not start arguments.

So, back to my overbearing roommate...
Ever since we moved in together, she has always told me how skinny I am and how I need to gain weight. She weighs 15-20 lbs more than me. It is impossible for me to skip a meal around her. Every time she eats, she insists I eat too. I try and tell her I'm not hungry, but she just shoves food in my face and tells me I need to eat more because I'm too skinny and I need some "meat on my bones". It's gotten to the point that I've been thinking about purging more and more lately. :(

And god forbid I ever want to exercise. She yelled at me when I told her I spent an hour on the treadmill! She said I don't need to be doing any cardio because it will only make me thinner, and if I INSIST on working out, I only need to only lift weights so that I can "gain muscle and bulk up".
I don't think she is doing any of this to be mean. It's just her personality. She's like this all the time. But it is really starting to get to me. I don't even like being in the same room with her when I change clothes. She always looks at me and says "oh my gosh you're so thin! Why do you even work out?" Maybe it's because I don't want my entire body weight to consist of fat... And she always makes me stand in the mirror next to her and compare leg size, arm size, stomach size. It's annoying, and it makes me uncomfortable. Yes, I am smaller than her. Why does she have to point it out all the time? I am in control of my own body, not her. Why do I let her drag me through the mud day after day about my body? I wish I could tell her all of this. But I'd never be able to work up the courage. I'm just not a fighter. I can't start things with people.

I know she isn't saying these things because she is concerned for me. The way she says them, I can tell it's because she gets jealous. She always talks about how much she hates her own body and wishes she were smaller and then turns around and tells me I need to gain weight. I think she just wants me to be the same size as her so she doesn't feel so bad about herself. She weighs 125. I am currently fluctuating between 105 & 110. I feel like I would be doing a whole lot better if she weren't interfering so much. How do I get her to stop? I don't think I can take it much longer...

HELP.