Bleeding 6 weeks postpartum??

Okay so my bleeding stopped at 3 weeks PP Me and my husband had intercourse at 4 1/2 weeks postpartum and today (Sunday) I spotted? I'll be 6 weeks PP on Tuesday... What was the spotting ... I'm freaked that I could be pregnant again... My doctor told me as long as I wasn't bleeding and my lochia was clear and it was comfortable for me that I could have sex... Could the bleeding still be my post partum bleeding just on and off ? Or my period starting up?