Bleeding after sex

Sometimes after sex not all the time when I go pee after there’s a very light amount of blood sometimes lasts for about a day after usually seems to be in the middle of my cycle. I’m on the pill have been for about 5 years recently switched to a new one a few months ago because the other one was making me heavily bleed middle of my cycle. It’s stopped with the new one but now recently in this. I’ve been with my fiancé for 4 years we got tested at the start of our relationship and both faithful so not an std. anyone had something like this before snd know why it happens? I’m small and hes slightly above average I’m usually pretty wet but sometimes it does hurt a little like it’s pressing on something