It's impossible to say. Tests these days are pretty good and if you waited until after you realized your were supposed to have had your period then that is like 3 weeks which i think they should be able to tell by then.
If you are 14 i am guessing you haven't been getting periods for that long? When you're a teenager they can be pretty irregular, especially the first few years so it's totally possible that you're not pregnant and your period is just late. I remember i used to skip them all the time. I got my period when i was 12 and even 2 years later they tended to be fairly regular but occasionally i would just skip a month or two.

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Because we're hotter when we don't give a damn