Hello Doctor, Good Day! Please I Saw My Menstrual Period

Hello Doctor, good day! Please I saw my menstrual period on the 20th March 2015 but had sex before the period started flowing! I took postinor 2 during my period flow which made it last a bit longer! I was supposed to see my period on the 14th, I have not! l have had unprotected sex on the 1st of april up until now... I have done pregnancy test thrice, through simple urine, it says negative! I don't know what to do! If to go for scan or wait a while