Actually, the most common cause of tremors is something simply called a benign tremor. They are more common the older we get. One of the other entities in this consideration is Parkinson's Disease. Doctors are trained to tell the difference between these two entities. Those are the two most common neurological causes of shakes.
Diabetes with low blood sugars from too much medicine, too much exercise or too little food would come with other symptoms such as sweating, heart racing as well as anxiety.
If the only time you exhibit these shakes is when shooting, I believe I would be hard pressed to know the cause of that as a physician. Medical causes for this should be evident in other activities as well. If it doesn't occur at other times as well, it may be a bad habit negatively reinforced over time and may be a symptom of recoil sensitivity. Lastly, there may be a possibility of peripheral nerve compression like carpal tunnel aggravated by the recoil. Doctors should be able to diagnose that by a physical exam, but in this condition I would also expect other symptoms at other times as well.
If it is only an isolated issue when shooting, then practice with dry fire at home might be a way to start to overcome this issue.
i hope this gives you some place to start.