i had this feeling when i was on the pill. are you? don't know what it is about the pill, but when my b/f would cum inside me it would burn like crazy. as soon as i went off the pill the burning stopped.
i had to go on the pill for a month a year or so after i went off of the pill...just to re-regulate my period. when i was on the pill the 2nd time, same thing...burning like mad when he would cum inside me.
now we just use condoms. no burning.
it could be that you just have a fine cut down there too. tell us more so we can help.
jasmine