5 year old with skin bumps

When my son was 2 years he developed a red bump on the back of his leg.  Doctor thought it was infected and we tried antibiotic cream which seemed to irritate it more.  After we left it alone for a few weeks it cleared up and left a brown flat spot that eventually faded.  In the past 3 years he has had multiple other spots all in different locations on his body.  Sometimes he won't have any and then he will have 5 in different areas.  They are a deep red color when they first start and eventually turn to brown.  Pediatric derm thought it was mastocytosis and didn't feel it was necessary to biopsy at that time (which was 2 1/2 years ago.)  We have appt with specialist this month but just trying to look into this more as he has about 7 areas that are in different stages on his body.  They do not seem itchy.  Any input would be appreciated.

Thank you