I am pregnant, just wondering when it is that i became pregnant?

I had my last normal period at the very beginning of april, and ive always been very regular. On april 20th i had my IUD taken out because it was becoming very uncomfortable and a lot of cramping so i got it removed and planned on getting a new one after my next period which shouldve been in the beginning of May, on May4th i had very light bleeding and it went away after 2 days so i wasnt sure if that was my period or because of my iud removal, that has never happened to me and im wondering if i couldve already been pregnant, I had taken a pregnancy test before May 4th and it was negative, then my june period never came and i found out i was pregnant, i havent been to my first doctor appt yet because they went by the day of my last period which i stated as may 4th???? Just wondering.