My partner and I keep getting this one pimple in our genital every couple of months randomly,

It’s one pimple and it hurts to the touch, it’s white and you can pop it.

First he got it on his balls then his inner thigh,

His popped it once and then its been gone?

At first we thought it was because he sweats a lot during training, but then I also got one on my outer labia and now I’m wondering if it’s something more then just because of shaving/sweat and general hygiene.

Could this be an STI?

Has anyone experienced something similar?