Bleeding after sex

Hi I'm on the pill, have been for two months now and my first withdrawal bleed came on time between these two months. I take my pill every day at the right time and my partner pulls out when we have sex.
Yesterday we were a bit rougher than usual and it was a bit uncomfortable, after which I noticed two small blood marks on the bed and some pale blood when I wiped. Would this have just been due to the sex? We did it once more after this and no blood? Thanks.