M.H.
I had a bizarre rushing sound in my right ear while I was pregnant, and a pounding all the time that was so distracting I nearly couldn't hear. I got no answers whatsoever, but imagined that the increased blood volume caused some kind of vascular issue.
When I get a sore ear like yours, I just joke that I slept on it wrong. Perhaps it's also related to the vastly increased blood volume. You could try one of those contoured neck pillows, I have one and haven't had nearly the sore ears I used to get when I bunched a pillow up around my head. (if acid reflux is bad and you can't sleep flat, try propping the mattress up, but still use a contoured memory foam neck pillow.)