Cysts in the labia - possible causes..?

I'm pondering an old Q-
Back when I was a teenager, I had a sexual partner (oral only) and I developed painful cysts in the labia that lasted only for one episode.

Here's the story of the things that happened to me around that time:

I had two silver Amalgam fillings clunked into my bottom left molars that june.

During that july, I visited my boyfriend.

When I got home in the first few weeks of august, I developed sensitivity at points in my labia, and after 5-7 days, the spots became painful swellings in the soft tissue in the labia. Most became the size of large peas.

They were sensitive enough that it was hard to walk comfortably in jeans, and I finally got annoyed enough to take a sewing needle to the swellings. I was shocked and quite worried when I managed to pop the first one (they were subdermal) because it let out a lot of pus (white blood cells) and red blood. When the cyst was drained though, it was no longer painful, and did not come back.

There were about 4-7 of them in total, and that was it.

I'm wondering what could have caused those infections. I suspect an oral bacterium, since I didn't get other STD symptoms.
Has anyone here experienced something similar, or have a suggestion of clues? Tweet