Can doctors misdiagnose a yeast infection?

I had a pelvic exam, pap smear, and std test recently, partly because I had what I thought was a yeast infection. The doctor called to confirm that it was in fact a yeast infection and gave me a prescription cream for treatment. Well, the infection has returned less than a month later, so now I have prescription for Diflucan (oral pill for yeast). But I have a fishy smell down there and it makes me think it may be BV...but wouldn't the doctor have seen that from my samples? How could a doctor miss that?