You were on your period, and you were in the bathroom crying because of the pain (and hormones that make you have special 'urges'). Ghost 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 knocked on the door to respect your privacy, but he had the key to the bathroom with him. Little devil, is everything okay in there? Whatever it is, you can tell me, I promise I won't judge you.