Welcome to healthcare Magic!
It seems you grip the pen very strongly and write with pressure.
Just collect the pages you have written recently and see the back, if the written text can be felt on the opposite side then you are tiring your muscles due to excessive pressure.
If not so then get your serum electrolytes levels- sodium, potassium, magnesium
, calcium, phosphate.
Some times low potassium and low calcium can cause muscle nerve
irritability and such problems.
Get this work to diagnose the problem and let me know.
Taking pacitane is not a definite solution only a bit relief.
I hope the advise would be informative and useful for you.