Wetting the bed...?

Hi,

I'm really embarassed by this so please keep it anonymous.

This morning when I got up I noticed a yellowish patch on my white sheet. Now I had registered over the last couple of months the presence of a few such patches, but assumed they were sweat or ejaculate (though I don't know why it would have yellowed, I think I sort of assumed the light made it look yellow). But this morning on closer inspection I found to my horror that there are a *lot* of these little patches, they're all clustered around where roughly my cock would be in the night, and they're definitely quite yellow (they can't be ejaculate).

I'm 22 years old and I never wet the bed when I was younger. Obviously I'm horrified and quite disgusted. Can this be anything *other* than me wetting the bed at night? If not is it normal for someone of my age to suddenly start wetting the bed? I'm quite ashamed and obviously I've changed my sheets but I'm no longer exactly enthusiastic about the next time my girlfriend sleeps round...