Breastfeeding & periods??

Amber • Mommy to miss Norah (3 1/2), miss Finley (1) and pregnant with a baby boy due in January!
My LO turned 7 months old today! Although I have exclusively breastfed her since day 1, my period came full force when she was 3 months old. Ever since, I have gotten my period every single 30 days. Well here I am 9 days late! I took a pregnancy test Saturday and it was negative. Could my period delay be from the breastfeeding or could I still be pregnant? Did anyone else get a period while breastfeeding and then it go away?