Hi I don't have any answers for you but I have a kind of similar problem. I had my baby in the middle of june and had 2nd degree cut and some internal tearing. (I ddn't heal very well or quickly - blood clots and burst stitches) My scar is still uncomfortable esp when i'm having my period. But it feels more like its bruised and a bit itchy. I assumed it was because of the increased blood flow and that the skin was quite thin and still healing.
If its stinging and you as you said you havent had any problems with it before this it might be an idea to get checked by your GP. I know thats probably the last thing you want but it's better safe than sorry, as they say!