oreosmum

Hi there, My dog has this more than a week, it became more visible day by day. He licks it sometimes and I am not sure he feels pain or not. Checked some resources on internet then we thought it maybe caused by mite/flea/spider bites. Anyone has similar case with this? *** the bump is red, if you look further you will find out there is a black dot in the middle of the bump. p.s the yellow is the treatment oil from the pet shop. Rear right leg