Suggest Cure For Constipation & Eating Disorder

Hi can you tell me why when I eat or drink, my stomach, lower abdoman, my whole belly gets really distended looking like I am 9 months pregnant sometimes. I have had past eating disorders, but have pretty much overcome it, have done some stupid things like overdosing on tylenol and poatassium a few times and i am on a few antidepressants and sleepers at night, but don't think it could contribute to my problem. I'm 32, 5'6" and weigh 115lbs, but sometimes can fluctuate to a 122 lbs in a day, and think I am just getting fat, but then comes back down when I fast. I don't feel any pain, but everything just swells up. I don't have any diahrea and only occasional constipation. I eat a healthy vegetarian diet and exercise regulary. I was just wondering if anything could be wrong with me. Thanks for any advice.