oh lol, this problem is easy. You are overworking yourself. Dont work out as much and you are right about the gritting teeth problem
Ur scrot hurts cos it is just growin pains and when u jack it makes you relax and forget about the pain. So to solve your problems, just
1. eat a healthy diet,
2.stop overworking yourself, take a break
3. If jackin feels good do it,
most of all tho-rest.
Get all the sleep you can!!! Dont stay up 2 l8 with the hand movement. If problem still persists pm me. Hope to be of help