What Is The Irregular Spotting And Cramps While On Birth Control?

I have a normal menstrual cycle. My last period was April 14th it was very light, mostly brownish and a little red. On April 22nd I had cramps and pink spotting as if I was to start my period again. The spotting was only once when i wiped. Now on April 26th I have the cramps and pink spotting again just once. I am also on birth control pills for a year now. I never had spotting before. What is going on?