What Causes Pain Behind Left Ear In A Dairy Intolerant Person?

I get a nagging pain behind my left ear, right where the end of my glasses sit. I had it checked out a couple of years ago and nothing seemed to be too much to worry about. I am 74 yrs old and it seems to be happening more often. While at the osteopath one day it happened, and she massaged the area and the pain went away. I said I would try that next time and she said to be gentle and not too much. It worked once but not really any more. I know it has nothing to do with my glasses. I am dairy intolerant and wonder about muscus causing the problem. can you enlighten me about what it might be. thank you