I had similar bleeding after my mirena was removed. It wasn't my period. It took my body a few months to get regulated again. Some women don't have any issues and get pregnant right away. Just keep testing for another week or so and then if nothing happens...you might be like me and have to wait a while for your next period. Good luck!
It could very well be from the BC, however I know many girls who have gotten pregnant while on the mirena, if your worried have a blood test done to make sure!
After I stopped taking my birth control pill I had one period, then I didn't have a period for two months. My doctor said it's because the birth control suppresses the uterus lining so much it takes some time to have another period. That could be what's wrong with you. I'd take a home pregnancy test in a week with first morning urine to be sure though.