Pregnancy test question!

So my husband and I were intimate 3 days ago and he came inside me. I was just wondering when I can take a pregnancy test? I have 2 laying in front of me right now and all the box says is I can take it 5 days before my expected period but that's the problem, my periods are irregular! So if I have conceived, how many days after unprotected sex would the test be positive? A friend told me I should wait 11 days but I just want to know what u guys think! Thanks in advance! :)