If you're too shy to see your doctor (which is my recommendation too) you could simply stop swallowing. Jump up quick and run to the sink and then rinse with water before swallowing at all. If the problem persists then you probably have no choice but to stop oral sex or see your doc.
If they problem persists, see a doctor. Also, they have these great flavored condoms at Wal-Mart or any grocery store. They come in great flavors for oral sex and he can go in the condom so you don't have to swallow. Your partner should understand if it is bothering you to swallow and should compromise. Hope it goes well!
I would suggest trying to swallow semen from a couple other guys just to see if you have the same reaction. If you do one recommendation is allow him your bf that is to ejaculate in your rectum which would require no condoms or birth control and he would enjoy it as much as you swallowing the semen.
i dont think telling someone from a post thats from 2005 to go around and swallow the semen of different guys is really the best advice. and no anal sex should require condoms to protect from stds