All 3 of my daughters had it as well. DD1 had a mild case which was limited to her thighs and bottom and resolved itself within about 6 months. DD2 had them the worst. Arms, legs, bottom, and a lot of them. Each one would become sore and inflamed before it cleared up. It was horrible. She had them for at least 18 months. Multiple trips to the drs and was always told the same thing, it's harmless and will resolve itself or we can burn them off (I never considered this an option for her, to traumatic and would scar). DD3 has them now and it's been over 12 months. She has a very mild case limited to her bottom, there's about 3 left so should be gone soon.
I feel so bad for your DS it has been going on for so long and he still has so many I wish I had a miracle cute for you.