Hello~It sounds like a pinched nerve to me, sometimes with those, your pain can be spasmodic, also, sitting down can cause pain as you might be impinging that particular nerve more. If it continues, I would see a chiropractor, they are great at releasing pinched nerves. He/she will probably take an x-ray of the area first however, study it and then go over the results with you. After a few treatments, the pain should be lots better.