Have you been stressed lately? Has life been quite busy and you've had alot on? Because that can disrupt your cycles. When i got married, afterwards my AF was late by 10 days! I thought I was pregnant but turns out it was just the 'happy' stress from the whole wedding ordeal. I wasn't stressed at all, but rather just busy with life....

Try and wait 3 more days then test again, if negative and no AF by then, go see a doc and ask for a BT for your peace of mind.

Good luck hun. I know it's frustrating isn't it.