I think you will find you are overgripping the bars ,and not doing the right things for distance riding here are a few I use and I can do 17 hours in the saddle.
RELAX
Grip the bars lightly you can easly control the bike with alight grip
stand on the pegs every 1/2 hour on long trips for about 30 seconds to keep circulation going properly
flex shoulder arms wrists fingers knees legs feet and toes when you can.
make sure your gloves and jacket fitt properly with being too tight .
wear a kidney belt and see if it helps .
most important move your head and eyes around regularly
try listening to your music ,some people find this helps some hate it up to you .
walk about when you stop to refuel
use painkillers like Advill/ asprin whatever you normally use before pain sets in
enjoy riding leave your problems behind .