Consume Product

This has been something that I have been struggling for my entire life. Every time I study for a test or I complete a big project and I accomplish something very big it takes me months of downtime for me to recover mentally in order to start the process all over again and start something new. I finished building a chicken coop four months ago and I simply have no motivation to start any new projects like building my greenhouse. For some reason it's as if I only have a specific time window where I can get myself to do something. I have very low stamina when it comes to working hard, but when I work, I make sure I do a good job and I get it done in a competent manner. Same thing happens with school. I study hard for an exam, do great, and I am unable to study for the next few MONTHS and then I end up failing the next exams because I couldn't get myself to study. Even forcing myself to do a task during my downtime period causes severe psychological pain. The only thing I can do is go to the gym and that is once a week because my upper body is extremely strong and my training for the 4 plate bench press feels rewarding (I stopped doing legs by the way).

Any advice?