Pain in back of the skull need not be only migraine.
It can be due to various other reasons too
Few reasons could be
1. Sprain of neck muscles
2. Osteoarthritis
3. Any small injury to neck or back of head
4. CERVICAL disc disease
5. Infections in that area
6. Systemic diseases like Gout,
Diabetes
7. Problems of Blood vessels
8. Tumours in CERVICAL SPINE or Skull or brain
Most of the pain can be relieved with simple exercises, life style modifications, tablets