What could cause increasing muscle weakness in neck and constant aching weakness in upper spine area, hurts to hold up head, feels like neck and vessels are swelling, with pressure at base of head?

See doctor. See your primary doctor for a thorough history and physical. Tests or referral to a specialist or therapist may be suggested.
Possible . Nerve impingement in the cervical/ neck area, needs imaging study such as MRI of cervical area, possibly even brain. Have an evaluation as soon as possible to get relief.