What Causes Itchy Scab On The Elbow?

Hi, I have a mole like scab on my elbow, it has been there for a 3 or 4 days. Until I realize I have it in the exact spot on my other elbow. It isn t where all the skin is but to the side of it. It sometimes itches, but only my left arm s scab does. I put a band aid over the left arm scab, but I found on the band aid a brown/ cream colored puss or substance. It now looks like an open cut. It stings if you touch it or press on it. It is VERY dry around it, but only around it. - Kelly