If they are truly blisters, and not ingrown hairs, it could be herpes. Some outbreaks clear up quickly, others can hang on for what seems like forever. Some people have classic symptoms, other people don't even notice they have it. The blisters usually form in clusters, then evenually crust over and disappear. It doesn't really matter where the blisters are, you can get an OB pretty much anywhere. That is why condoms don't really protect you from herpes, unless the person has an OB directly on their penis or vagina.
You owe it to yourself and future partners to get tested while you still have what may be an active sore. That is when the test is most accurate. Go down to your local health dept. if you don't want to go to your doctor. They'll test you for free. Don't be embarrassed! It's the responsible thing to do. It may be nothing, but if it is herpes; the herpes board on this website has lots of good info and support.
Good Luck!