Burning on the outside of the vagina

I don't know what this is. I'm fine and feel completely normal. Until it comes to having sex. I use Durex flavoured lube with no condom.. When he inserts I have to take it slow because there's always a little soreness but then near to the end and sometimes afterwards I can feel a strange sort of but if but on the outside of the vagina. Does anyone else know what this is?