Taking progesterone-only pill: advice?

Lauren
Okay so I'm on a progesterone-only pill (Cerazette) and I was due on my period Wednesday just passed but it never came. This is first month of taking it and I'm about 2 weeks in. I know the progesterone-only pills are known to stop your periods altogether but I'm still suffering from my usual symptoms inc. severe cramping.
Has anyone else experienced this? What should I expect?