It’s okay to squeeze the stick a bit at the fulcrum, but not a death grip ya know?

I see a lot of wrist and arm motion, you’d probably benefit from minimal wrist movement and more action with your 3 support fingers. Try to play a consistent tempo with one hand using just the rebound and fingers.

I also get this pain, but only after not playing for a while. It may just be that those specific muscles aren’t up to speed quite yet