RnR - I get that really badly. It's basically a delayed histamine reaction. In my case I think it's an allergic reaction to the pool chem. Antihistimines will work. I used to take one about 30 to 45 min before swimming. I didn't like taking meds so often so I switched to swimming with a nose plug and that takes care of it.

Swimming with a nose plug takes a little getting used to because you can't breath out through your nose. Doesn't seem like a big deal, but it will feel really weird for awhile, especially if you're from a swimming background. When you're used to timing out breaths thru the nose during things like flip turns etc. you can sometimes blow your plug off!