Last week I hit my head on my steel bedhead and I have a headache on the left side and it wont go away, but comes and goes, what's wrong?

How hard did u hit? We used to think that post concussive syndrome only happened when you whacked yourself unconscious. Now we know that it can happen after seemingly minor head traumas. Any new-onset headaches, especially associated with recent trauma, need to be worked up by your doc.
See doctor. Several possibilities from subdural to neck spine injury etc need to be considered.