What Causes Pain Behind The Head?

My nephew grabs behind his head and cries as if he's in pain. Just randomly starts crying. I feel bad cause he is only 7 months. He doesn't crawl, roll over, nor does he push himself up in a push up position on his belly. It is almost as if he can't lift his head up. Should my brother be concerned. He just brushes if off and says he is ok to just leave him (nephew) that he is healthy.