something's wrong

So reciently I've come to notice during sex everything burns, like down there. And after sex when I go pee it burns like fire but the rest of the time it's 100% normal, like nothing's wrong; but I've come to notice also it's slightly itchy, but inside of that makes sense? My partner and I are exclusively us. We have no other sexual partners so I know it's not an STD.i don't know what it is, help?