Several years ago I was told by an orthopedic surgeon who happens to play a lot of golf (I know - they all do) that it results from trying to "muscle the ball". He suggested to focus on more relaxed muscles during a swing and more stretching for warm up. I now spend a lot of time at the gym working on "father time" and do a bunch of stretching and rotational exercises related to golf twice a week. It works.
Now, if I could just find an exercise that can help me hit the sweet spot more consistently!

I had the same problem. My pro told me that I was making contact with the ground with my trail arm bent. I started extended my right arm at contact and the pain went away after a few weeks.