Dear moms! Can anyone tell me if they've had something like this?

Dear moms! Can anyone tell me if they've had something like this? My baby is three and a half months old, we gave him his first vaccination that same day, after lunch I felt a small bump just above his anus, it's internal and kind of like a little pinch. It doesn't grow bigger or bother him when he goes potty - he doesn't cry! The doctor said there's no serious indication, maybe weak mucous membrane, but for safety's sake, he advised applying Levocetirizine cream. Has anyone experienced something similar? Share your experiences.