Welcome to health care magic.
1.The history is not very clear with nature of lump and duration. But according to your words it seems like a long standing and spinal lesion.
2.The possible cause could be any thing from a muscular lesion,
lipomas, spinal lesions, tumours arising from spine, any disc pathology appears as a bulge, or bony pathology, degenerative growth an so on.
3.At this point get an
ultrasound to know the nature of the lesion its contents, sours of the lesion and its extensions.
4.An lateral
cervical spine exercise to see the bony pathology. But bet tool to investigate is
MRI ( if no issue with affordability that will be the best ).
5.Finally if its a mass lesion an FNAC - fine needle aspiration cytology for assessing the cells of nature. Treatment depends on the investigation findings. Good luck
Hope i have answered your query.
Any thing to ask do not hesitate. Thank you.