I had surgery for a herniated disc three weeks ago. started having sciatica on my right side. now i am having pain in right arm and can not close hand?

Neck: You may have a new problem in your neck. Check back again with your spine surgeon. Sorry to hear you are having that.

See neurologist: Sometimes the body positioning during surgery can cause a nerve injury. This is similar to when you fall asleep on your arm and wake up, and your hand is numb. Because of the anesthesia during surgery you don't move, so the injury can be a little more severe, although most people improve. Typically these are painless weakness. You should probably see a neurologist for the appropriate testing.

Get evaluated: The new symptoms are concerning. I suggest prompt evaluation by your physicians.

Not Related: Hand pain and weakness is most likely associated with your neck and something going on there, possibly herniated disc or spinal stenosis. I would see the surgeon and have him order cervical spine MRI to evaluate what is going on in the neck.