It's always hard to gage. While there are more fertile times, you can get pregnant ANY time you have unprotected sex. However, the sex you had the day after your period started (the first day of your period is cycle day one and I believe you are saying you got your period on may 31, that was day one of your cycle, right?) would be a less likely time. The other dates . . . more likely especially april 8. I believe that would make you on cycle day 9 and that is when the more fertile window begins. Sperm can live for up to a week. You could be about to start your period, for sure. But otherwise, take another test. But with the next one, take it first thing in the morning with your first morning's urine. That has the highest concentration of HCG if you are pregnant. If it is negative and your period hasn't shown up for real, take another one one week later. good luck