You can get OT for problems with hands and writing.
My kids have hypermobile joints and low muscle tone so had problems holding the pencil properly, writing clearly and maintaining the posture to write for long periods. If it had not been caught early they would have had problems with writing for long periods due to resulting compensations in the way they write, causing muscle and joint stiffness.
A pencil grip helps if you have problems gripping the pen. Pinching exercises such as with a "pooey animal" and squeezing and pinching specialist therapeutic putty. Strengthening the upper body with push up exercises against the wall. But I would recommend seeking out someone who specialises in OT for hands and getting an evaluation.
But if you simply mean getting bored by having to write for long periods, not sure what the answer is to that.