How do I get myself to be more motivated?

Okay so a bit about me. I'm a high school student. Most of my schedule is a semi-routine (basically there's some routine but not always). I have some after school activities to prepare me for finals in 4th grade (the finals are quite complicated in my country) that I go to almost every day except weekend. My problem is that I seem to loose all the energy once I get home. I'm quite loud and energetic person whenever I'm at school with friends or on tuitions but whenever I get home I just sit in a chair for hours on end and don't do much other than watch things in the internet. I go tr bed relatively early and I would love to spend time on things I love but everything gets so hard for me after school. For example I'm penpaling with a couple of people and for over a month im trying to get myself to finish one of the letters but I have no energy to do so and when I try my mind just goes blank. I just spend all my time rotting away and I don't want to keep on living like this. I tried motivating myself with some sort of reward but it doesn't work for me. I don't want to waste my free time away. Does anyone know way to improve motivation enough so that I can actually focus on my hobbies?