What Causes Stomach Cramps And No Period While On Microgynon Pills?

I am on microgyn birth control and have been for the last 3 years. My period comes every 2 weeks then month then 2 weeks and so on like this. I was due my period 1 week and half ago but am late. I had light cramps couple of days before I was due my period but then nothing until the last couple of days when I have had constant cramps but no bleeding. can you please advise why this could be happening?