I have a painful itchy lump behind my left ear,right on the bone its been there awhile but it hasn't grown,within the past few months I have had terrible allergies and sinuses,what could this be?

Something you should talk to your doctor about.

Without seeing it, and knowing your complete medical history, no one could properly say what it is. Less so any one of us.

Talk to your doctor first before applying anything on it, it may increase the problem.