Hello a few weeks ago i engaged in oral sex. This appeared two days ago. What is it? Thanks

Hello a few weeks ago i engaged in oral sex. This appeared two days ago. What is it? Thanks

No detail in the photo to comment on as it is too dark. If you want to post other photos take them in really strong daylight …
From what you are describing this sound most like a Lymphocele, they are very common in this area. Usually they are linked to vigorous masturbation and / or sex