WTF?!?!?

My boyfriend is quite larger then normal guys I've been with. Everytime we sleep together regaurdless of the time of month (excluding period sex) there is white creamy stuff on his penis. I have a orgasam everytime we have sex but he and I are kinda like wtf is going on down there. Never had this happen but honestly never had a orgasm with anyone other then him. Any ideas???