Sorry to hear that you had a bad accident a few years ago that required some stitches over your eye, and that you have some persistent numbness
afterwards. I am happy to give you my thoughts as far as what might be going on, but if you want the most accurate answer, then I would recommend making an appointment with an ENT (Ear Nose Throat) physician, or otolaryngologist
for an exam. They should be able to give you a better idea after looking at you. Typically with a bad laceration that needs stitches, the physician (in the office, or emergency department depending on where its done) will inject some lidocaine to numb up the area so it can be washed well prior to throwing the stitches (so that you don't feel it). The anesthetic wears off within a couple hours, so there should be no way that it is contributing to your numbness a long time later. More likely, there is some crush injury
to small nerves in your skin over your eye that are causing numbness to the area. Typically these small nerves grow back in the weeks to months after the injury and there isn't much residual numbness however. Depending on exactly where you hit above your eye, it is possible that you injured your supraorbital nerve (a branch of cranial nerve 5...V3 specifically) that gives sensation to that side of your forehead. If the area of numbness is quite large, then my guess is that is likely what happened. In any case, it is important to speak with an ENT physician.