nine,

You could easily have messed up hormones. My wife is about your age and has her bio-identical HRT adjusted by blood test once a year. There still is some cycling. Add a concussion and it can get more problematic.

Have you had any chiro or PT manipulation of your spine at C-5 to T-3? this area can be inflamed and causing the stomach problems. Been there, done that, dealing with chronic stomach issues. Fortunately, I know how to treat at home if the problem is minor. Ice and an exercise using a large rubber band.

I have had this problem on and off for 20 years. Resolving the spine issue has always solved it or at least reduced the intensity.