When I move my right arm up I get a sharp pain at the top of my neck/head on the left side, what does this mean?

Cervical disc. You may have a cervical disc problem. Pain in the neck and associate arm pain or pain with movement may very well indicate a significant problem with your cervical spine. It could be other things but i would see my pcp or orthopedist or neurologist and get an evaluation. You many need imaging and other testing. I would not delay this evaluation.
Pain in arm. Sounds as though you may be having referred pain from your neck and you may be experiencing a herniated disk please have your neck thoroughly worked up for a disc at c5/6. Hopefully, it is just a muscle spasm but referred pain to the arm could relate to the neck and/or brachial plexus. At the same time severe shoulder pain can sometimes radiate to the neck.