some people have spotting when they're pregnant. when i first had sex it really messed up my cycles, i was 5 days late and i started spotting, i thought for sure i was pregnant but my period ended up coming.
i know its hard but you need to stop worrying, haha i know that sounds silly. but since you've been stressing it's probably causing your period to be delayed. (eh?)
it could be because you might be pregnant... so i really think you should wait a few more days, test and if it still comes out neg then go to the doctor, there's nothing else that we can tell you here hun. but you can stick around and give us updates.