most likely it's one of the tonsillar lymph nodes.
I get the same thing. it comes and goes...sometimes mine hurts. I was told its just a lymph node that can become infected.
It's glands, you have quite a few glands in funny places, the most common are under jaw on sides of neck, you notice them when your throat is sore, but there are little ones that are marble like/ atleast in my case right behind ears. I think this could be what they are, not sure why they swell up, my son who is 22 gets them all the time, there for a while then gone. His DR, says nothing to worry about. I hope this helps.