My daughter was recently sick and developed a sore under her nose, which we thought was caused by the constant nose blowing. It hardened to a scab and fell off, but before it did, a sore showed up on the edge of her mouth, which is now in the process of hardening. At the head(?) of it, you can see yellow discoloration, as if there is puss underneath the skin.
I'm sorry for the poor picture, but it seems too dark to take a clear one.
Any suggestions as to what might be the cause of this?