Thanks for posting your query.
The muscle stiffness
in your neck and dull pain may be related to muscle spasm. A physical examination is necessary to find out the exact cause.I suggest you to consult an orthopaedician nearby for a detailed examination.
The treatment usually involves rest with pain killers in combination with the muscle relaxants along with good physiotherapy
Meanwhile you can do a hot fomentation and apply a local analgesic
gel on the area to relieve the spasm.
I hope this is helpful to you.
Wishing you good health...