I think your nerve compression is progressing and this is why you are feeling weakness and inability to do these work. I would suggest you to get a MRI of the cervical spine ( if plate and screws are of titanium) And it will show us if there is any nerve compression is there. I am afraid in that condition you may need a revision surgery. If there is no nerve compression then you can safely take Pregabalin and Methylcobal tablet daily and also wear soft cervical collar. it will help in gaining strength . Though it will take some time.