Although such things are probably best not mentioned in 'polite society' this can be a problem for us singers - I've had the same problem myself. A couple of months ago I was talking to an old mate of mine, who used to be a favourite singer at one time, and he mentioned the same phenomenon.
I've found that drinking lots of water, especially when the room is air-conditioned and over-heated (far too many are these days), can be a great help. I've not found any OTC medicines or herbal remedies but I might try some of those mentioned above (now, where do I get slippery elm bark?).