What Causes Menstrual Cramps But No Periods After Taking Postinor 2?

Hey, I used postinor 2 3times on the 15th 17th and on the 21st of january and am yet to see my period I have been having regular menstrual cramps and sometimes I wud see a reddish brown stain on my pant please help me its febuary 7th and am still having normal cramps but no period