Used to get a similar thing all the time. The MD's told me it was due to what I was drinking (alot of soda). I figure, someone in your shape probably stays away from that, but lots of BB's that I know drink craploads of diet coke. Anyways, anything with a high acidity content would do that. It feels like a tingling/slight burn that remains even after you pee. Check your diet and see if you're taking anything with lots of acid in it. Even lots of vit c or that damn hearburn in a bottle ALA could do it.