What Could Be Causing Undiagnosed Tremors And Numbness In My Left Hand And Arm?

I am a 31 year old Female, with undiagnosed tremors in left hand. Sometimes there is Numbness/ tingling in left arm. I ve had 5 Mri s an EMG and a spinal tap that all came back normal. My Neurologist and Physical therapist have no clue as to why. Any guesses?