I get a rash, same place, though doesn't sound like it's as bad. I noticed it happened *under* those nifty Zoic knickers, so it wasn't sun (thought maybe the shorts rubbed off the sunscreen or something). It'll stick around for a couple days though it fades.
Yea, I would make a Monday appt and ride a long one on Sunday (tho' I might try shorts rinsed nicely in something hypoallergenic first).