I had sex and started my period right after that means there is no chance I could be pregnant right? I don't have an STD
Lets just say it is very unlikely that you are pregnant.
In most cases, the egg would not be viable just before your period is due so the chances are extremely remote. There is always a chance however.
i would wait a week. and take a PT. if you didnt have safe sex than its always a 50 50 chance. good luck!