Rashes on leg

Hi Mummies, my little one who is 13mth old. Had a switch to S26 stage 3 progress formula not long. Recently we see some mosquito like bite bump appearing on his feet on both legs. Could it be allergy to the formula? He have been taking S26 stage 1 and 2 since birth, and there is no issue till we switch to stage 3.#advicepls #pleasehelp