Trigger points (TrPs for short) can cause referred pain - this thread has info & links showing how to locate trigger points..
http://neurotalk.psychcentral.com/thread125577.html

I get sore spots on my scalp , it actually gets lumpy in the soft tissue layer, all from soft tissue/ trigger points , sore muscles.
I work on the muscles/TrPs and the lumpy sore spots fade away..