I had the exact same problem my hands hurt, and I had real bad forearm cramps, I would death grip so tight I would sprain / injure my hands and wrists.
Aside from brusing my ribs thinking I didn’t need a rib vest, it was the worst injury I received from karting, jumping right into shifters right off the bat was part to blame.
what I have noticed now that I have just over a full season to reflect on is:
Adjusting your grip thru the course will help immensely.
I noticed that along with gripping the wheel like my life depended on it, I was also tensing up my whole body which will wear you out fast.
Also a good setup, fresh tires, brakes etc. will help, fighting a bad setup or worn/dried out tires will also wear you down.
Try to relax, you will find that as you get better with setup, remembering to breathe, adjusting your grip, etc. you will end up being able to drive fast with a lot less effort eventually, that’s when karting will start to get really fun and extremely addictive!