From your description the symptoms seem to be a Neurological problem. One of the possibility which needs to be considered is a Myoclonic jerk where things can get dropped from your hand.Its difficult to confirm without more details or witnessing the movements. If its occurring again try to make a mobile video clip of the shaking with help of a family member or friend so that it helps the doctor decide. Im sure your neurologists have already ruled out a parkinsonian tremor
I also suggest you take another opinion from a Neurologist again, probably from a Teaching hospital or a University hospital if at all possible.Hope this helps.