I don't know anymore?

I'm 17 and try to stay positive in life as much as I can and recently been able to keep myself in good mood. But no matter what I always go back to having the same demeanor of being bitter, angry, and cynical. I'm doing really good in school and my parents are great I have great relationships with my family and friends so why do I always feel like this? I know that life is better when I'm positive too I just always slum back down and I know that one reason is that I am a perfectionist but that is not always the reason.