How do I prevent vomiting? I have an intense fear over vomiting. I want to do whatever I can to prevent it.

What makes you fear? Before one can prevent something one has to figure out what might be causing it. Sometimes it's not possible but one has to try. Prevention is so much more effective when one knows what to block or get rid of. Your doctor or an experienced counselor can help figure that out. It doesn't seem medical. You may need to have a psychiatric evaluation and medication, but take it one step at a time.
Vomiting phobia. Not that infrequent, it can cause many associated fears includiing: reluctance to eat in public places, food aversions, marked decrease in oral intake if exposed to someone with the flu, fasting, school refusal, easy gag reflex, frank avoidance of those who have had the flu or who have it, sympathetic gag/vomiting, and catastrophic images of what might happen if they were to vomit. Emdr works.