Scalp on back of head red and sore rash. 2%D72 inches. Causing puss build up in hair. Like stabbing needles. Suggestion what it is??

Folliculitis. This may be an infection of the hair follicles and since there is purulent drainage, warm soaks followed by application of an antibiotic ointment like Bacitracin is the usual treatment. If the area swells, increases and becomes more painful and tender, see your physician for possible antibiotic pills and/'or incision and drainage if needed as it would be treated like a small boil.
Exam-folliculitis. call your phuscian or get checked at an urgent care center- this is a bacterial scalp infection-you can use some baby shampoo until seen.