It can be really hard to stay motivated in school, especially as a senior in high school. I had the same problem in my senior year as well because I felt as if I was already done with high school, taking SAT/ ACT, and applying to colleges.
Some things that helped me stay motivated was reminding myself that I am almost at the finish line and that my friends are going through the same thing as I was. Also understanding that if you finish strong, graduating high school and receiving your diploma will feel so much more rewarding. At times you’ll feel extra unmotivated, and that is okay! It’s okay to have to work on your mental health and it’s okay to take breaks. Just remember that it is important to maintain a balance between school and mental health.
I think that you need to have to know what the end looks like. You have to have a firm vision of what you will be doing once you have finished your college work. I did not finish college right away when I first went. It took me 17 years to get my bachelor's degree because I couldn't really see what my future would be like. I did start working and I found what I loved to do in my work life. And for a long time, I didn't need a college degree to do my job and make good money. The challenge came in my 30's when I was laid off at a time that my career choice benefitted from having a degree and I didn't have one. All of a sudden, I was not being hired on my experience but turned away because of a lack of a degree. So when I finally had this hurdle - not able to do the job that I love, I got serious about college. I ended up getting a Bachelor's degree and then a Master's degree. I knew that I wanted to do, so every time that it got tough, I thought about my goal.
Now thinking of your goal may not always work. It can be two to four years away. It is too far. So you need to focus on reducing the stress of college. Motivation goes down when stress goes up. So mitigate that stress with stress management activities like working out or just going and doing things for fun like hanging out with friends or taking a vacation. In college, you have control over the courses you take (mostly), so make sure that you take courses that interest you. Interest can be a short term motivator that gets you through.
Try and be successful