Bf always moody after sex

It can't be a past experience, because we were both virgins before we started having sex together. He is quite a naturally moody person, and he does have moodswings, but he is always still loving to me, he just goes quiet. But after sex he's always the same, really off with me, and kind of like as if he doesn't want me to be there anymore. It is getting me down cos it's making me feel a bit used almost. As if he's fnished so now he's not interested. But then the next time I see him, like the next day or soemthing, he'll be completely back to normal.

Like I said, I'm going to talk to him, but I don't want to upset him, I just don't know whether it's normal!