Hi, Nancy, the real question is who you slept with closest to May 16. You were given the "weeks pregnant" or Gestational Age by a medical person. If a doctor, nurse, or any medical person says you're 6 weeks "pregnant", it is not a figure that counts back to conception but to two weeks before conception, to the first day of your last period. All medical counts of pregnancy (the number like 6 weeks 3 days or 11 weeks 4 days) begin two weeks before conception in order to line things up with the assumed first day of the woman's last period. If a doctor says to a woman, "Congratulations, you are 6 weeks pregnant!" he means 6 weeks since her last period began and about 4 weeks since conception.
The count is done this way because the period is a big, obvious signal, not because the doctor thinks you are pregnant when you are on day 1 of your cycle. (The doctor knows you were not pregnant then -- you were having a period!) But that is why pregnancy, which takes 38 weeks, is counted as being 40 weeks long. They add a spare two weeks at the front to be able to calibrate the count to the presumed first day of the last period.
So, don't spend a lot of time trying to decide between a guy with whom you had sex on May 2 and one with whom you had sex on May 5, look to around May 16. It would not be the guy from May 2 unless you had sex with him later.