My partner and I have have been together for awhile and have only had sex with a condom. Both times I ended up with this blister spot down there that burns really bad. It's so sensitive that I can't even shave right now.
Difficult to tell without a picture but a couple of points worth making:
Latex allergy can be a problem with condoms so you might want to try with non-latex condoms.
Condoms arn't good at protecting against Herpes, so just because you used a condom doesn't mean your safe. So if you think it might be Herpes get yourself to the clinic asap where they can swab it.