What Causes Brown Vaginal Discharge And Abdominal Cramps?

hi for 12 days i have had brown clots disharge and abdominal cramps.i am taking microginon 30. I had missed a pill two weeks ago then the discharge started and now im having abdominal cramps. I did have sex on my last pill break about 3 weeks ago. i had also missed the last two pills in my last pack.could this be an infection or a pregnancy?