How did i test positive for and std and my boyfriend tested negative the last time ive ever been with anybody else was january (except i got fingered in may while i was drunk) i only found out about the std because of a pap smear during my pregnancy?

Some basics: Your pap smear likely showed evidence of HPV, one of the most common STD's but not part of most "STD screening tests", especially for males. Prior to the vaccine as many as 70% of college age women showed evidence of prior infections. The non-wart strains generally have no symptoms in either sex, but in women some strains can trigger cervical cancer years or decades after the initial infection