I can only eat for less than 10 minutes at a time, then food repulses me. Help?

I can eat for usually about five minutes, and then all of a sudden if I smell food or think about food or, heaven forbid, eat food, I feel like I have to vomit. If I try to keep eating I gag and have to spit it out. It's more prevalent with foods of a certain texture; foods like pizza and lasagna and basically anything that isn't crunchy makes me think of eating human flesh. But it's with crunchy stuff sometimes, too.

I had an issue with starving myself a few years ago. At that point I was doing it to lose weight, got down to under an 18 BMI, but now the urge to do it is sporadic, like once every few months when I start feeling depressed or something, and in between those times I only starve if I need to maintain the weight I have now, but I'm very active so it's not usually a problem. Anyway, my mom thinks I might have shrunk my stomach during the almost three-month period when I restricted my calories. I don't know. This was never an issue before then, and it didn't become an issue until a couple months after it, so I don't know.

I'm open to any theories. It's really annoying when I can't eat for more than a few minutes. I had this amazing barbecue pulled pork sandwich from Subway that I had to throw away three-quarters of. Someone please help, thanks.