You wrote, 'I still keep angrily chewing at my nails.'' Sounds like you understand the cause pretty well, if only by intuition. Human nails are like the claws of any animal -- they can damage and, after damage, they contain residue. (Come to think of it, unlike non-primate claws, primate nails contain more residue, since primates use their nails to feed, while animals use their teeth.) So, you intuit that the issue is aggression. If you are still in school (I gather from what you say), you're a young person and are still learning to master aggression. Aggression is especially a problem for teenagers in our society because we demand so much independent achievement of them. Anyway, the chewing would be to inhibit aggression and the cleaning would be to clear away evidence of aggression. We all do this to some degree; nature provides a way to symbolize it in chewing and cleaning, and with that knowledge we can work out what we're so angry about.