There is a blue/black spot under my big toenail and i don't know what it is. i removed my nail polish today and saw it, and am now very concerned. ?

Photo documentation.: A black/ blue spot under the nail in a 16 year old is probably nothing more than a bit of dried blood trapped under the nail. This could be the consequence of a minor bump of the toe of a pressure injury. Without actually seeing it, I guess it could be something else, but I doubt it. To remove all concern, you might have a physician take a look at it.