You were on your period, and you were in the bathroom crying because of the pain (and hormones that make you have special 'urges'). Mike was obviously worried because you had been in there for a while and had locked yourself in there. After waiting for a few minutes, he decided to check on you, so he had the key to the bathroom with him and he opened the door without knocking, pulling you into a tight embrace, showing that he's concerned without saying anything.