I have a hard-ish lump on the back of my head around the hairline. it is the size of a pea and you can move it. hurts to the touch. should i be worrie?

Exam needed: This could be an ingrown hair, inclusion cyst,wen or benign fatty tumor(lipoma). A lymph node in that region is less likely. I doubt serious pathology, but a physician or dermatologist would have to examine you for diagnosis and advice. The tenderness could be simple irritation or infection, and that is why you should check it out. In the meantime apply warm compresses.