Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
If your tremor only occurs with writing, your symptoms may be consistent with what is known as task-specific tremor. This is a type of tremor that occurs only with specific actions, such as writing. This may be a component of task-specific dystonia, what is termed in the medical literature writer's cramp. This is due to involuntary contraction of specific muscles during actions such as writing. It is generally benign, meaning that it does not typically progress to involve other body parts or lead to other problems, but it can sometimes involve more than one task, and it can lead to impairment in function, such as you describe above. Sometimes, treatment can be successful with injections of botox into very specific muscles to slightly weaken those muscles without affecting overall hand function.
If your tremor occurs with various tasks such as eating or if it even occurs if you just hold something or hold your hands up in the air and it is a fine high frequency tremor, it may be consistent with essential tremor or other types of tremor. Many types of tremor are treatable with medications.
Evaluation by a neurologist, and if available a neurologist with expertise in the field of movement disorders, is recommended.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.