i recon you scrubbed a little too hard and scatched yourself ! soap would sting a scratch ,you really need to use condoms mate there are some real nasties about to catch . stop by your docs get tested to make sure it aint too late !
Yeah, as SeriousSam says it doesn't sound too serious, but maybe you should hit the ol' doc just to put your mind at ease... better safe than sorry, eh?
It could be std but most likely it's just chafing on a new area.