I know that you love your girl-friends but I would not be the one to let tell influence you, I'm 13 an 5'5 1/2 an I wiegh 187 an my doctor says im helthey so I geuss what im trying to say is that to mite want to go to a doctor beafor you try to lose more weight. good luck :-)
I'm a bit disturbed at your writing that you are 5'9" 125 pounds and your mom is urging you to lose weight. You don't need to lose weight and it sounds like your are developing an eating disorder and your mom is encouraging that. Not good. I would talk to a counselor at school and get a referral to a therapist experienced with eating disorders. That therapist can alsom meet with your mom and talk with her about being a positive influence for healthy eating not supporting eating disorder behavior. Please get help before it gets worse.
Your stomach cannot hold onto food out of choice, but your body can. If the meal you ate was already being digested then there would not have been much left to vomit. When there is nothing left in your stomach and you are still throwing up, you will start seeing bile/acid. Acid is produced in the stomach when the body is hungry. The feeling of your stomach "eating itself" is how most people describe feeling overly hungry because your stomach is very acidic.
The trick to healthy weight loss and avoiding starvation mode is to eat frequently, but with the right kind of foods. (No Mick D's!) That means lots of raw veggies, lean protein, and whole grains. The fibre will keep you feeling full, the protein will feed your muscles (and boost your metabolism) and your weight will find its happy place. You definitely don't need to lose, so just focus on staying healthy okay?
:-)