Well, if you had a head injury, then yes, that could be the cause of the pain. At times a nerve injury or a leaking blood vessel takes time to produce symptoms. Hence it is important to get this investigated, first by an eye specialist, and then by a neurologist.Apart from this pain in the eye can be due to ocular or ophthalmic migraine, glaucoma, stye, sinusitis, eye infections, eye strain as is seen in refractive errors (if you cannot see properly and need spectacles).Since I cannot examine you and know other related conditions you may be having, nor is a detailed history possible on net, I have listed the various possibilities that should be looked into. Please consult your eye epecialist.Take care!