She might have a yeast infection or an upcoming period. You better put some rubbing alcohol on those fingers man.
try the shower thing first. if that don't work, reffer to rule 2 2. if you smell it before you eat it, take a hint and beat it.... (just like to state for the record, i love preforming oral on a woman, but that's a big rule. I wanna be going juicy not clumpy.