Mouth pimple or herpes?

About a week ago, I got a single growth on the inside of my lower lip. It died down after a few days (it seemed to be irritated by the mouthwash I use) and then when I started using the mouthwash again, it flared up. I tried popping it today, thinking it might be a pimple, and it bled. I've been looking online about distinguishing characteristics between mouth pimples and herpes -- it seems rare to get mouth pimples inside the lip, but it's a single growth, which makes me think (hopefully!) that it isn't herpes, which usually clusters. Are there more signs I should be looking for? Is there something I can definitively do to judge whether it's a mouth pimple or herpes (short of seeing a doctor; I'm not in my home state right now and am staying here for a pretty short while, so I'm reluctant to go through the hassle of finding a physician). Sorry this is such a gross question. Thanks for any help!