Me and my SO had sex the last week of Nov. he then was gone until Dec. 30. I had a "period"…

Me and my SO had sex the last week of Nov. he then was gone until Dec. 30. I had a "period" Dec23-26. it was very light and that's not normal for me. I had a baby Oct 25,15.

I just barley got a positive test Friday. my Dr office is thinking I'm 4 weeks and 5 days but that doesn't add up to when I would have gotten pregnant. do you think I could have gotten pregnant during Nov. but why would it take this long for a test to come up positive!

can implantation bleeding last that long?