Pregnant. Saw Brown Discharge. Can It Simply Be Implantation Bleeding?

first off do i have to pay I am wondering if i am pregnant. my period was due yesterday but all i saw was some light brown discharge . it didnt smell. this morning i was blood but it has no smell or clots. usually when im on my period there is a smell and i do have lots of clots. I dont know if this can be due to implantation bleeding so this is why i need help. me lasy period was july 11 2012 and i ovulated on the 23. i have had unprotected sex three days before i ovulated up until the day i ovulated. my next period was due aug 5, 2012 which was yesterday but, like i said all i saw was light brown discharge. i have been having headaches , feeling vomity, having extremely painful lower back pains and lower abdominal pain for the past weel. can you help cause i need help.