Looks like an allergic reaction. Try some hydrocortisone ointment and see a dermatologist.

Dear Sir/Madam, for the past few months, around about the middle of my menstral cycle I develop this itchy rash on either one or both my elbows. I am 41 years old and have been taking asprin for nearly two years - low dosage (unfortunately I had a very small heart attack nearly 2 years ago). I'm not overweight, don't smoke have low to normal BP and Cholest of 3.9. Never found an answer why. Please can you advise if you think the elbow thing is related to any of this - I've never been allergic to anything before - My gut is hormonal and aspirin related. sincerely Sara