Hello~I agree with the other poster's answer, it may be a reaction to any meds you may be on, asking the pharmacist is a good place to start for answers. If meds are not the case, then I am strongly thinking you may have a thyroid condition, this will certainly cause the hair to fall out as well.
You say you are 14, well, at this age, the hormones are all over the place, so, this could also be due to fluctuating hormones.
If you are on medications, check the side effects - call a pharmacist if you don't have access to that information. Certain medications can cause hair loss. That's a good place to start.