Pregnant earlier?

My periods are normally 5 days. In October I had 1 day of heavy bleeding and the next day nearly nothing then what would have been the 3rd day it was completely over. Then when it came time in November no period and a bfp. So right now I'm estimated 5 weeks going by the "period" from october. I read a woman had the same thing happen and wad actually further along than the thought. Has this happened to anyone else, could I be further or do you think that was really my period in october? I did take a test in October and it was negative so that's where I do believe I wasn't pregnant yet but the woman that said it happened to her also had a negative.