blue belt, just turned 40.
I suggest you look at your life outside of jits. Is something bothering you? Depressed? How is your nutrition/sleep?
Years ago when I was doing JKD I had separated/dislocated my shoulder but didn't really realize what happened. All I know is that it was painful. I lost the desire to train. I was a little stupid and kept trying to push myself though. When all interested in training left, I would ponder why.
It wasn't until it popped back in place months later that I realize it was my body telling me that something was wrong.
Fast forward to this year, had a separation with the wife, split custody with the kids, 5 deaths in the family (not at the same time) including two grandmothers, my interested waned.
Kept trying to jump start interest in training. Went to a different school, varied what I did, etc, because I know how happy jiujitsu made me. But it didn't help.
Finally, after I hit 40 this year, I decided to cut out coffee, cigs, alcohol and no to MJ. It took about 4 days for my body to really start feeling better, but it did.
I think that for me, I was just not taking care of myself, abusing myself. It wasn't much, but with all the stresses in life, I needed my body in optimal condition to also train.
STOP EATING WHEAT.
Have you checked if Low Testosterone might be the culprit for your lack of mat mojo?
Go to a Seminar with Rickson Gracie and you will be motivated again. Not just by his techniques but by the way he sees Jiu Jitsu as a developement for life.
Also if you train with some older masters like Roy Harris or Joe Moreira you will see that these guys are killers on the mat even with 50 and that you have plenty time to get better in BJJ and learn.