Eh sayang, that stinging feeling after 3 years baru keluar is quite common lah, sometimes the scar tissue from normal delivery can be a bit sensitive still, especially when it meets water or urine. A few of us mums went through the same thing and it eventually settled down on its own, but since yours is persistent and making you worried, better check with your gynae just to be sure there's nothing small that needs attention, ya? They can assess quickly and put your mind at ease!