A "flat affect", like you're describing, can be a sign of depression. Or it could be something else - or maybe nothing more than being teenager in the present moment.
It sounds to me, like you should talk to someone about that. Whether that's a parent (initially), or a doctor, therapist, psychologist, or psychiatrist - you should let those who care for, or are treating you, know exactly what's going-on with you internally. Otherwise - they probably won't be able to guess, and the situation may continue to go unaddressed. So above all, be honest with yourself, and those who care for, or are treating you, about how you're feeling.
Here in LA - we just lost Brody Stevens. He was brilliant and hilarious, but was dealing with a bipolar (1) condition, and issues with medication and treatment. The world will find a way to go on without him - but it will be less joyful and rich, because of his loss.
We ALL have at least one something unique that we bring yo the world - and perhaps many things. You may not yet have found all of yours just yet, but in time, you certainly will. Stay strong, and stay in the struggle, until you prevail, over all your personal challenges. We're here to fix what's broken in the world - even if that's something internal, within ourselves.