I would definately go and see another doctor for a second opinion. However, It may be just stress. I have similar symptoms (trembling left arm, sometimes numb, sometimes with pain), and these are mainly at night and are caused by stress. 'But i'm not stressed' you may answer, however the physical symptoms of stress can be present even though you feel mentally happy and ok. Shift work can cause it, as well as life-changing events like moving house or a divorce or a death. I have managed to overcome mine to a great degree by eating better and going to the gym. Exercise is a great stress-buster. Anyway, go and get it checked out first, and good luck!