New Mirena insertion

Let me start this off with saying I have never been pregnant. I had the mirena iud inserted on July 13 and on July 24th had unexpected unprotected sex. Up until the 22nd I was having some cramping and some spotting, even had my period. Spotting and cramping began again on the 27th. I am aware that the mirena can not be in full effectiveness for about the first month. Is there a chance I could be pregnant?