i'm not sure if this works or not, but i've always heard to bd before and day of O, but i've been doing that for over a year and it hasnt worked and both DH and I are healthy and fine. The one time we bd day before, day of, day after and two days after O we had a chemical. This cycle we bd before, day of, day after, two and 3 days after O and we will see in about a week if it has worked or not. I think some people may have a temp rise when the release the egg and some men's sperm probably only last for maybe a day before dying off so if you bd after O then the sperm have a better chance of getting to the egg.
now im NO doctor by any means i'm just throwing a thought out there. I'm testing my theory as we speak