How long have you been primal? How strict are you?
I ask because it sounds like you're still converting from being a sugar-burner to being a fat-burner. (The transition took me a good 3 months or so!)
Stay the course, be sure to eat enough, learn to listen to your body, and you'll find that you're able to go longer and longer between meals.
I have noticed in the past that Aunt Flo can sometimes make me hungrier than usual. An extra serving of protein (particulary beef, maybe because of the iron?) is generally sufficient to cure that little problem.