Why do I have random burst of rage and anger?

I have been having massive bursts of anger for no reason at all. It only happens when I am alone but Its just this insane amount of anger and rage, I feel like I could tare someones head off. It happens every 2 or 3 days, sometimes more and has been going on for about a month. I am also perfectly healthy, I have been to the docs recently and had my blood tested I have no problems with my physical heath. Mentaly I feel fine and i have a happy life, I have no clue what is wrong with me. If it helps to know I am sixteen.