That's how I knew I was pg this time round, couldn't drink wine, and it was about a week before I was due on - I did do a test then or thereabouts, got a negative, a week later a BFP but I suspected all along because I 'felt' pregnant. Look at it this way, if you test early and it's negative you haven't lost anything (bar cash) you just have no further information either way and have to do another one a few days later! Good luck!