I have sudden pimple like rash which appeared on the lower back of my leg, began itchy and as healing is dark red dots slowly fading? picture added

Exposure to plant..?: Have you been hiking... short pants...,insect bite? Are pimples more like pus? Spring time is very common to encounter plant which can cause rash ( poison oak & other). If itchy Take antihistamine, topical steroid cream for 7-14 days. If increased pain , spreading redness .. see MD to check for infection ( cellulitis .