Numbness at the back of my head and i get really sensitive all over.not sure but i think i hit the back of my head 2 months ago.its off and on..

Get it checked out.: You've got to see a doctor and get this evaluated asap! you might have just pulled a few muscles back there and bruised yourself but you also might have done something to your neck vertebrae and so be one jolt away from a serious neurological injury. So go see your doctor fast, get examined, and make sure it isn't serious. Good luck!

Nerve injury...: Possible explanation of your persistent pain is injury of " posterior occipital nerve", branch from cervical spine supplying back of scalp with nerves to feel. If injured it may as if " fire " signals as pain rather than touch etc. It is called " neuralgia".I may go away but if not consult your doc.

Could be from the: Bruising or could be a minor pinched nerve from arthritis in your neck spine. I won't worry much unless there's increasing headache, numbness/ tingling /weakness of arms or legs, nausea, vomiting etc. You may take Motrin (if no allergies) and apply warm packs in the meantime. Go see your dr for any worsening symptoms. Take care!