Hello and welocme to HCM
It is difficult to comment that your problem is psychological or not.
However, there could be an organic cause to it.
Muscle wasting, muscle weakness
can be a cause of inability to write.
Besides nerve involvement due to various disease processes can be the cause.
You need to get investigations checking muscle and nerve functions eg electomyogram (EMG) and nerve conduction study
Consult a neurologist
for the problem for clinical examination and for investigations.
In case these tests are norma,l you may visit a psychologist
Thanks and take care
Dr Shailja P Wahal