My 4 Yr Old Son Has Been Having Small Itchy

My 4 yr old son has been having small itchy insect-looking bites around his private areas (particularly between his buttock cheeks and sides/behind his scotum) for about 6 weeks. We've taken him to our local doctor a few weeks ago and ruled out pinworms. The doctor wasn't sure what it was but prescribed mupirocin and betamethasone valerate to help clear up whatever was causing it. This helped get rid of the existing "bites" didn't prevent new ones. They honestly look like some sort of small insect bite and cause him to scratch all the time. But they are only to be found in his private area (nowhere else on his body).