Mirena question??. help.?

I had mirena iud inserted may 19th i had my son march 30th.. My doctor told me to wait 2 weeks til its effective. But everything i read says its effective right away..i wasnt on my period when she inserted my iud but i had my period on n off after i had it in. .my question is if i can have unprotected sex with my boyfriend c*ming inside me now is the mirena effective?. Thursday was exactly 2 weeks n today is saturday we had unprotected sex today..y did i have to wait 2 weeks?. Sorry if i dont completly make sense but anything u all may know will help alot. Thank you and please no mean comments .