I feel so fat all the time and can’t stop thinking about food. I have urges to throw up after meals. What can I do to change?

Thoughts of purging and obsession with food may be early symptoms of bulimia and other eating disorders. These behaviors are both physically and emotionally unhealthy. If you feel that you are unable to control these thoughts, consider talking to a trusted adult or a therapist.
Learning ways to develop a positive body image and focusing your mind on other activities/hobbies besides eating can help to change how you feel about yourself. Exercise has been shown to improve mood (by releasing endorphins), suppress food cravings and aid in weight control.
 
For information on healthy eating, weight control and building a positive self- image:
https://www.teensincharge.org/topics/nutrition-and-fitness/eating-right/
https://www.teensincharge.org/topics/nutrition-and-fitness/weight-control/
https://www.teensincharge.org/topics/emotional-health/body-image/
 
 
Reference:
http://www.helpguide.org/articles/eating-disorders/eating-disorder-treatment-and-recovery.htm