You only think you do. Thinking is the problem.
Look closely and you might notice that doing homework doesn’t stress you out. Thinking about doing homework stresses you out.
Look closely and you might notice that you’re less happy on a Saturday night than you are sitting in class on a Tuesday afternoon. But you didn’t notice that because your thoughts about Saturday night make you more happy than your thoughts about class on Tuesday afternoon.
There is a simple way to break this cycle: actively notice what’s happening right now. Notice your thoughts and notice how they make you feel. Over time, you can train yourself to have new thoughts, and attribute less importance to the ones that used to make you feel bad.
The process is simple, but like most things worth doing, very difficult.