Hey Iwant2bethin! Gosh, what a rough time!!! But I don't think you have gained all those pounds of fat unless you have also been eating like there's no tomorrow. Could be water retention from stress. Also, are you near TOM?
Well, about your mom. It sounds like she is worried about her health--you should encourage her to see a doctor. It does sound like she's having a hard time, even if it is dramatized. Maybe she does this a lot? I don't know her history at all, of course.
You have a choice about whether to escalate into an argument. You can't win an argument about who has had the rougher day, so just go on without taking the bait. I realize it's hard because this may be a long-standing pattern between you. Still, you can try different approaches. Tell her you're sorry she's not feeling well, express your concern that she may need to see a doctor, and then if she's still wanting to fight with you, you can tell her you don't want to fight and go to your room. Or go to a friend's house if it's possible.
Meanwhile, you need to stay away from using food for comfort. Easier said, but you gaining weight is not going to lower your stress or make your home life better. Get a supply of good snacks like vegetables, and get rid of the chips, candy, chocolate, ice cream, or whatever it is you turn to.
Can you talk to anyone at school, like counselor, about your home life? Or do you have a trusted adult friend or relative or maybe a pastor or rabbi you could talk to about your problems?
Good luck! It's a tough one!
"My religion is kindness." --His Holiness the Dalai Lama