A blood test can tell you the answer. I'd also make sure that i am having once yearly PAP smears to test for HPV which can cause cervical cancer if left undetected (there are 4 particular strains of HPV that are implicated in the cervical cancer link).
And you're right - you could already have herpes and be asymptomatic. I'd make sure you are using a condom and see a doctor for the appropriate blood test.