I Had A Child On August 8th 2016 And I

I had a child on August 8th 2016 and I am roughly 5.5 weeks postpartum. My fiance and I have had intercourse a handful of times since my son was three weeks old. The first time was August 29th and he ejaculated inside of me. I took a pregnancy test today and it showed negative at first but about 5-10 mins later it had a faint pink line. I came back about 30 mins later and the line was gone. Is there a chance I could be pregnant this early with a positive pregnancy test? Or could it be left over hormones from pregnancy?