They make tests that can show a positive up to 4 days before your period is due. I doubt you'd be having symptoms of pregnancy this early though. Those are caused by hormones and if you don't have enough hormones to get a positive test, you probably don't have enough to cause symptoms. However, never say never. Let us know the result!
I've had what I think is implantation bleeding since thursday I will give it a couple more days then do a test