I actually understand where you are coming from with this. My mother does this to me all the time. The worst part for me is I might be 30 lbs overweight, but she's way more and I'm being lectured about MY weight.
There was a Dr. Oz a while back which featured women who were way overweight and while I didn't see the whole show, I caught this one part where a psychiatrist said the first question you have to ask yourself is who told you you were worthless. Immediately I think "my mom." And this one lady goes on about how this doesn't apply to her cause she had a great childhood and you find out that she was molested and her mother knew about it and let it happen. Obviously for that lady, that question is vital cause she doesn't even consider that an issue. Then there are the people like me (and possibly you) who go, "it's my mom cause she does it every other day" yet that doesn't seem to help the issue.
My mother likes to point out things and then say she's doing it so we don't look dumb in public. Personally though, it's just annoying cause I'm not 6 and there is a reason behind a lot of what I do that she doesn't consider. Like the one time I came from the basement in a tight tanktop and capri pants and was told I shouldn't leave the house looking like that and that I smell. The fact that I had just worked out for an hour in the basement and now was heading to change and shower didn't even get considered, or the fact I was sweaty and out of breath. I just get a "honey, don't wear that out of the house, it's too tight. Ugh, you smell. Did you put on deodorant today?"
So yeah, kinda got sidetracked there for a bit. The best I can say is try not to let it get to you, find someone to rant to about it when it does get to you, and don't worry too much about your weight. If it bugs you then try to work on it but don't do it for your mom. Another thing to try is telling her it bugs you. Doesn't work all the time, since my mom still tells me things that I've said I don't want to hear anymore, but it might get her to realize that it's hurting you.
If you are going crazy with food, it could be that you are missing something in your diet and trying to make up for it with other things. Try adding nuts as a snack cause they are full of vitamin E which is great for your body. It's difficult if your family is eating pie while you eat a handful of nuts, but it can help. I know there are other things that are recommended but I can't remember at the moment. If nothing else, you can try to maintain your current weight until you move out and then work on losing it when your mother isn't there telling you how bad you look all the time.
I know it's frustrating but things will get better. If nothing else you might find that person that loves your booty and then your problems will be solved.