BFN, Postpartum, Late Period

I am 7 months post partum and have been having a period regularly the past three months. My husband and I had intercourse during my fertile week. I've been having symptoms like I did my first month of pregnancy with my son and my period is two days late. I've had some barely there spotting yesterday and today. But I took a couple tests and it's BFN. Does this sound like just a normal symptom of postpartum maybe?