I think before all else, you need to learn about what districts you and what interests you.

Like for instance, can you play a video game for 10 hours? Can you binge a whole Netflix show in two days?

Look at common things about such stories and try find novels that have the same effect on you.

Reading in general, is about discipline. There are times when I can't put a book down, and other times where just like you, maybe I'm reading a sentence over and over again and not getting anywhere.

Why does that happen? Maybe I'm at the coffee shop and I'm getting distracted by two people having a loud conversation. If I put in headphones and play instrumental music, it allows a kind of droning rhythm which helps me focus better. Maybe I'm sleepy or our of energy and I need to position my reading as one of the FIRST things I do in the day and then save more fun things for later when I'm low on energy.

When it comes to school, really you just need to have some perspective. Are you so weak that you can't force yourself to sit still for one hour at a time for the benefit of your future? Is your brain so limited in its processing power that you can't convince yourself why something can be interesting even if you're not passionate about it?

Really, there are two possibilities before you. You need to learn to be consistent and do things even when you don't want to do them, or you should probably drop out as soon as possible before you go to college for 6 years, get no degree and a 1.9 GPA.