Well if you came back on a blood test negative and you would be about 6-8 weeks then I would take that as your answer. Blood tests are rarely wrong.
Depending on your age and how long you have been mensturating for.. When you last had sex, emotional factor and all that lot could all have other reasons for your peroid not coming.
Have you lost or gained a large amoutn of weight recently?
Are you under alot of stress?
A recent change of situation?
Had sex for the first time (has been known to make people skip a peroid)
if you have only recenntly started your peroid in the last say... 8 months or so it may still be trying to ge in a a routine and just out of whack.
I really doubt your pregnant because of your negative results.
But the you stressing out over it will also delay it.. Secondary to being pregnant, stressing over thinking you are pregnant is the most common cause of a period being late.
Hope this helps