IB or AF?????? Help!!!!!

Okay im not supposed to start my AF til Sunday (08.16015) im almost always right on time and it's always has been very crampy and heavy but today (08.14.15) I am having some light spotting when I wipe I put a pad on to monitor the spotting but no blood goes on to the pad sorry I know TMI . I never had IB with my first 2 pregnancies And this is our 4th cycle trying to conceive im 12dpo so could this be IB and if y'all think so any one with experience know about the average it last or when I should possibly test if the spotting does not become heavy???? TIA