Pregnant but confused HELP!!

Ok so October of 2015 my fiancé and I decided to have the IUD took out! I started to get periods 5 days long with a 28 day cycle. November, December and January I got my period like I normally do! Had unprotected sex on the 22nd of January but got my normal period on the 26 all the way til the 30th light and very heavy days. So Monday I took a pregnancy test only to come out negative. For some reason I took a digital one Tuesday and said pregnant 1-2 weeks on the 11th of February I also had unprotected sex with my fiancé so my question is when did I get pregnant?!!!