Small pea size solid lump on nape area of head?

Uncertain. Please discuss concerns with physician. It is not possible to determine what the lump is without an exam.
See doctor. That should be looked at by your primary care doctor or a dermatologist.
Identification . You did not provide your age, your race or your sex. Is it a single lesion, tender to touch or drainage. Did it occur after using chemicals on your hair?
Probably cyst. Most small lumps at that part of the upper neck are sebaceous or other benign cysts. They sometimes are painful and should be removed. If asymptomatic and not growing, they can be left alone. If they become infected, the may need to be lanced and removed after the infection clears if bothersome.
Benign or malignant? See dermatologist or surgeon for biopsy to remove it and send to pathology. Physical exam may reveal other lumps so a more thorough work up will be indicated. Could be a benign sebaceous cyst or something more serious.