I keep nodding and shaking my head a lot and i can't stop. what should i do?

See neurologist: Could be tic, tremor or possibly tourette syndrome or another neurological problem.

Tremor: A variety of neurological conditions can cause head shaking. If a no-no direction, this could be due to familial essential tremor or hyperthyroidism. If in a yes-yes direction, could be a cerbellar titubation tremor. A disorder called wilson's disease may cause tremors, and many other conditions could be considered. Medication reactions may be an issue. See a neurologist.