It is probably sensitive because it never healed correctly since you stitched it up yourself, etc.

I cut my left forearm quite badly in Feb 2011, as in right into it by accident (as in I wasn't supposed to cut that deep, but my skin was soft from being wet in a hot bath), I needed roughly 20 stitches and whilst I did get them do at A&E (ER) I removed them myself a day or two too soon since I didn't want to book an appointment with my doctor to get them taken out, now I have a horrid noticeable scar there and it is sensitive to heat/cold.