Confused.

Kayli • I am 28. Married. And have a 6 year old, and 2 year old. Pregnant with my third.
I had a baby about 3 months ago. I started birth control on New Years (the non hormone one while breast feeding) and had one period a week later, I was supposed to start again a week ago. Is this normal? Or could I be pregnant again? 
Anyone have this happen before?