Another "could I possibly be pregnant" ?

Ok, so here is my situation. My last period was on March 25 and I have a 31 day cycle. I have not gotten my period. This past week I have been feeling very nauseous and my husband noticed I was having a heightened sense of smell (I never made much of it, until he mentioned it). So I took two pregnancy test and got a negative on both...so what could be going on? Has this happened to anyone? Thanks