If you've had unprotected sex and you have normal periods, there is always a reason to believe you may be pregnant - tubal or not. Your chances, obviously, are decreased, but not completely gone - it has happened before.
You're stating that you're 6 days late - most home pregnancy tests are sensitive enough to pick up hcG in your urine now. If you take one, the results should be fairly accurate - however if it is negative and within a week you haven't started your period, it is advisable to make an appointment with an ob/gyn in order for them to run a blood pregnancy test.
Until you know for sure the best thing to do is to treat your body as if you are - no smoking, drinking, or medications.
Good luck!
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Thanks,
Marki