need help

ok so i had sex july 7 and 8 and mt period was supposed to come the july 10th. It is over a week and i still havent got my period and i have tested several times and nothing. i also have regular peeiods and always come but have had 2 miscarriage a while back. it is to early to test positive or could it be something else? i have changed my eating or havent been on birth control and im bot stressed more than usual. please give any advice