Hey, actually, many people do consider overeating a disorder. Basically, because it is a symptom of "something." In the majority of cases, over-eating is a symptom of "emotional pain."

I used to see a nutritional therapist who told me that most anorexics and bulemics go through a period of time when they sway to the over side and gain a ton of weight. It is almost expected as they deal with emotional issues and start bringing up issues, people eat more to "push them down."

I am also Bipolar and take Lithium and Seroquel. Because of the Lithium, my thyroid is shot. I have gained ALOT of weight too. It sucks.

I goto this support group and the phrase is:
"Fat and happy, skinny and sad." meaning that everyone who is on bipolar meds is fat. It sucks.
Plus the meds make you crave more sweets, make you thirsty, and some make you hungrier. Additionally, there is some belief that they alter the metabolism, so it is easy to get fat.

I wish I had some good advice for you ...just know I totally relate!