Confused.... Please help

Stephanie
Ok so my cycles usually come around the 5th of each month. In late October I got really sick with a severe kidney infection and a uterine infection which the e.r. Dr never told me what type it was just said there would have to be more testing to be determined, anyway my period was screwed up that month...there was just light spotting (I actually thought it was implantation bleeding, but Dr said I wasn't pregnant) so November I didn't have a period, December I had a very light one only 3 days at the beginning and the same for January. On January 27th I got a BFP and the line was very dark...showed instantly and this test was taken 5 days before I thought my period would be due. With as messed up as my period was, I'm confused as to when I might have conceived. Anyone have any ideas???