Go to the doctor &get a bloodtest.

Are you under large amounts of stress? Believe it or not, I have heard that stressing yourself out causes hormones to delay your normal cycle. This may be true especially if you are stressing about the possibility of being pregnant. You may want to take the previous poster's advice and go to your ob/gyn, they'll do a blood test to hopefully give you a more definitive answer. Good luck

That has happened to me twice, and I would have to say that both times it was due to stress. I tested after being a week late and then at two weeks late both times, and got negative both times (it was amusing right after the 2 tests, I got my period lol). I am now somewhat regular again.

Now, I am in my late teens (19), so I don't know, I might be going through a change in the regularity of my period. If you are around my age, that might be what you are going through? And some women are never regular no matter how old they are.

Like arcadia said, get a blood test, they're more accurate.

Hoping all is well
~krystal