My first day of my last period was on 2/10 it last 4 days, I usually have a 32-33 day cycle. I was feeling sick so I took a test on 3/3 it came out negative I did have intercourse that night again. I missed my period and took a test on 3/19 and it was positive. I was trying to see if I conceived prior to 3/3 and it just didn't show because it was too early or if it happened after 3/3.