I have a 5 month old daughter who has extremely sensitive skin the day she was born. She has to use certain laundry soap, bath soap, wipes, diapers, etcetera. Last night I noticed some redness on her bottom, I lifed her up to look closer and found a quite large (about the size of a nickel) circular scab with a small hole in the middle thats filled with pus. As I touched it, she screamed. It felt quite swollen. What could this possibly be?