When was my conception date?

My LMP was 4/1/10 My periods are usually regular & every 28 days. I have been trying to conceive for a couple months now & have sex every other day, my ovulation was approximately around 4/15/10 and I started testing on 4/26/10 but all the tests came out negative. I stopped testing on 4/28/10 because I got what I think was my period. Since then I only had sex once and my period is now late, should have came on 5/27/10 but it didn't so I took a pregnancy test and it came back positive! My question is did I conceive in April since I was having sex every other day and what I thought was my period on 4/28/10 might have been implantation bleeding or did I conceive in May even though I literally only had sex once that month? I know I'm pregnant, I would like just to know when did I conceive so I know how far along I am?

[RockRose]

This is really something your doctor needs to figure out - there could be anything at all going on here,  including the possibility that you ovulated weeks later than you thought.