The pain for Pancoast syndrome generally is more common along the forearm and hand (particularly the ring and pinkie fingers) rather than on the clavicle. The presence of a mass in the lung causes compression on the nerves and produces the syndrome. It is unlikely that a mass could suddenly grow to a size that would produce symptoms in a span of 3 months.
It would be best to discuss your symptoms at length with your doctor. An investigation into the specific nerve distributions where the pain is felt is a step to start with. There are some maneuvers in which an arm and neck position may favor compression of some nerves, or some blood vessels, and in so doing produce the pain symptoms.
If you are a football fan, could it be there is previous trauma?
First thanks for the comforting response. I am trying to stay positive through out all of this. Next, I haven't played football in a few years. So I don't think that would be the problem. My favorite team is doing well so far, so I haven't thrown any remote controls. However I am remodeling my house. So between carrying and hanging drywall, painting, tiling, plumbing, etc, I suppose I could have done something. Although I don't remember anything specific, I supposed I could have done something.
IF you have access to some specialist care, you could consider seeing a Rehab (other places call them Sports medicine) doctor. These specialists are very thorough and are able to isolate specific muscle groups during the examination, so if it is indeed more muscle than nerve compression, we would know.