on birth control - Could I be pregnant?

I started birth control last month on November 15th, I took my pill every day at 4pm. I never missed any pills. I have a 28 day cycle and my periods have always lasted for 5 days. I started lightly bleeding on December 9th and it only lasted 2 days. I've been having very mild cramps on and off since then. It is now the 18th and still no period... Could I be pregnant or is this common for the first month of birth control? I had a miscarriage 5 months ago at 14 weeks. It was very hard for me. ... So, if you're wondering why I sound so paranoid...