Hi Carol!
I'm 53 and have had this problem occasionally...especially when I'm on a diet and eating more healthily - more fruits & veggies. But, I also have IBS - do you know if you have this? You say you drink "lots" of water - I don't know how much that means, but I can tell you this...on those rare occasions when I'm constipated, my Dr. recommends drinking a lot of water!! MAYBE you're overdoing a bit with the H20???
Fatty foods can also cause diarrhea - I can't tolerate donuts, haven't for years. LOL I would try eating more starch, maybe mashed potatoes, noodles, bread, etc., and see if this helps...but don't overdo them, either.
One thing about IBS, it really doesn't matter too much WHAT you eat - I have gotten diarrhea eating cheese, and constipation eating lots of fruit. it's more about the spasm of the bowel. And there's a bit of some strange connection to the colon and the stomach - sounds weird, but there's something about eating that stimulates it.
The other things is...as we age, so does our whole GI system. Mine has been bad for many, many years. I belch a LOT. I can belch on plain water and/or with an empty stomach.
I know none of this really helps, but at least you know now you aren't the only one so afflicted.

I would talk to a Dr. about the possibility of IBS. There are meds that can help...and maybe ease up on the water a bit, too, especially if it's a bit excessive. Take care!
Hugs
Char