Hello! I apologize in advance for the photo, but could someone tell me…

Hello! I apologize in advance for the photo, but could someone tell me or anyone know if their child had something similar?! When the baby was born, there was nothing, around the third week when I massaged the buttocks, I felt inside like a small hard nipple, went to the pediatrician, said it was an infection, nothing serious, it will pass over time, prescribed cream, when I started using the cream, there was pus coming out of the place where this nipple was, it was breaking through. (Attached photo, almost 3 months old). But it didn't heal completely... Went to another pediatrician, said it would pass, prescribed an anti-infective cream. To this day, there is a mark on this spot