Dark, Itchy Circles On Inner Thigh Have Turned Into Pimples, Similar Patch On Arm. What Could The Cause Be?

Hi, last month i noticed two dark circles on my inner thigh one was raise and i suppose it was because i itched it, However, they look like something may have burned me, but i dont recall getting burnt especially not between my inner thighs and one of the circles seemed to have faded while the other turned into a pimple . I summed it up to maybe a that i was bitten. Today, Again I notice another similar small burnt circle and a tiny burn patch along my arm and now im concerned. Especially because i have not handled anyything that could possibly have burnt me Can you say what this may be please. Im so worried.