I have a small painful lump on the lower back of my head, it has been there for 2 days and has some redness, it isnt from an injury. what is this?

Cyst: It sounds like it may be a sebacious cyst.This would require removal and , if infected, antibiotics.

See your PMD: Bumps on the back of the head can come from multiple things, including trauma, as you mentioned. The redness can be a sign of bruise or infection. If it is hot as well, this could be infection. In non-traumatic posterior neck lumps, these are usually cysts or lymph nodes. See your pmd for a physical exam.