I am a recovering bulimic and now when I eat more than a little food, I feel like I'm going to throw up. Why? What can I do?

Give yourself time. Sounds like you're having trouble with your gag reflex, and you may be contemplating a return to old behaviors. Take your time, work with a counselor, and continue with small meals until you are comfortable with those.
Enlist some help. Many recovering bulimics find that after suffering from a history of purging, they find certain foods or large quantities of food difficult to tolerate. It may be helpful to establish a treatment team to maintain your recovery (and weight). Typically, having a therapist, good primary care md, and a nutritionist are helpful and may give you some good guidance on this problem.