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

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.