Need some opinions!!

Victoria
I'm 4weeks and 7days pregnant, my LMP was on 08/08/15 and I had sex with my boyfriend between the 15 and the 20, and I alhad sex with someone else one time on 08/21/15, I'm confuse and scare because I don't know if it's my boyfriend or the other guy. Any opinion on this? Please don't judge me I'm human.