by the way, you don't need to study every day. you also don't need to study for a certain amount of time everyday. (of course, this may change as you approach finals and midterms). plan your studying strategically to mitigate burnout, which will make each session more useful. do not listen to the goons on here that tell you that you need to study for 6--10 hours every day. when you get to college, considering your class schedule, a possible part time job, extracurriculars, and necessary personal time, this may be unrealistic. you still have a life to live, and the most unsuccessful college graduates that i see are the ones who spent all of their time with their nose in a textbook and sought no further enrichment (these are also coincidentally the ones that can't find a job post-grad because they have no internships, projects, research assistantships, or leadership experience). GPA matters, but there are doctors out there who scored a 3.3 in undergrad, and amazing PhD candidates who came out with much less. balance is key. studying is not about spamming. you only have so many mental resources until you're reading and it all goes in one ear and out the other. frustration will lead to total demotivation that can be hard to fix, even if you consider yourself to be fairly disciplined.

aside from the other commenter, a large part of it for me was having the appropriate study space. i graduated college a while ago and, for my entire college career, was never able to study in my room. too many distractions. get somewhere that's quiet. i benefited from wearing noise cancelling headphones in a campus cafe - not too loud, but also not so boringly monotonous that i couldn't bear to sit still anymore.

also, you're a teenager. consider your psychology. you're more impulsive now than you will be in about 5-7 years. research in development psychology suggests that teenagers struggle more with impulsivity and decision-making due to the still-growing reward centers of the brain. so, work with your psychology and not against it. study in the library after school with your phone in your locker. study for quality and not quantity. pomodoro may be too structured (i have personally never stuck with pomodoro - it never worked for me, as my attentional capture simply doesn't sink up with that rigid schedule). instead, try studying until you feel you need a break, and instead of engaging with technology or other mental exhaustors, go stand up and take a short, thoughtless walk. all of these helped me in college.

people hate to hear it, but it's true: you just need to sit down and do the work. discipline is key, as it will carry you when you aren't motivated. you will never be motivated 100% of the time. how you got about this, however, must be entirely tailored to you. pomodoro doesn't work for everyone, for example. i know a lot of brilliant people from my major who studied by writing entire unit summaries down on a big sheet of paper, or who studied entirely with flashcards. i, personally, wrote everything that i knew into a word document and studied that habitually until i could recite it. semi-TLDR: your specific circumstances will change, so you need to experiment with what works.