Focusing for a long time is not good for you. Your eyes will be strained, your posture not alligned, leading to a lot of discomforts and health problems. Try to focus for only 30 minutes to 1 hour, and be productive within that timeframe. Then get up, stretch, and inhale some fresh air outside.
Ars Nio Q.
I'm actually not that great at this either. But, when it comes to studying, I have this app called forest (possibly flora on ios) which really helps me out. It makes you that your not distracted by your phone. You should check it out❤️