I’m married to a Podiatrist, but that doesn’t make me a doctor, but I’m also a CNA at a hospital on acute care floor. Have you gone to your physician for this? I’m not diagnosing you, but maybe you need to go and ask if it could be cellulitis
It's summer and I get all kinds of weird itchy bumps on my skin, mostly the legs. If you I were you, I"d keep a close eye on this and I"d also buy some hydrocortisone cream or ointment from the drug store (no prescription required) and rub some on it to see if that makes it go down. If this doesn't improve, or it the welt gets bigger, OR if you develop any other symptoms like a fever (big red flag) then I'd go to the doctor, or a walk-in clinic.