Could it be a urinary tract infection? If so it is treatable with anti-biotics.

Or it could possibly be cystitis (sp?) which again would possibly need anti-biotics and cranberry juice available to drink (as well as his normal water) - this is no joke and is given to guinea pigs with the problem.

Other than that how is Fred in himself?

As it is a Sunday and I think you said you have some anti-biotics perhaps you could start him on them now and take him to the vet tomorrow.