can blister by genitals be something other than herpes?

I was  convinced that I have genital herpes. Once, after have unprotected sex, I got really painful blisters on one side of my vagina. they weren't on the vagina, but the skin right next to it. They were so painful, I was sure it was herpes. They were also very large.The blisters never crusted or anything,as far as i can remember(.this was 3 years ago and i was terrified so i blocked a lot out), They just kinda....went away.. I've had 3 tests (blood because I haven't had any other break outs since) and they have all come out negative for both types. If those tests are correct, and those blisters weren't herpes, what else could they have been? I've googled it, and there seems to be no other answer for blisters down there.

[gracefromHHP]

at this point you've covered your bases the best you can unless you get a return of symptoms. If you do get these again, go and be seen immediately for proper testing.

could've been friction/irritation, allergic reactions etc going on too.

grace