What Causes Frequent Shaking In Neck In A RA Patient?

I m a 51 year old female with Rheumatoid Arthritis since 45 years old. The past two years I have noticed my head shaking back and forth like as if to say small no s. It would happen every once in a while but since this past July its happening more often than not. I do have RA in my neck but this feels different. I get headaches in the back of my neck and the back of my head above my neck a couple of times a week. My head feels heavy at times like my neck isn t strong enough to hold it up. I do not have the shaking symptoms anywhere else in my body. What could this be?