How can I stop dreaming so much at night?

Every night I literally must have dozens of dreams, and my mind goes crazy. They’re not nightmares or anything, it’s just that there’s so many of them and it always has to do with the stuff I’ve been working on all day. For instance, if I have been doing math problems for the last 3 hours of the day then it will be a bunch of dreams related to math..

I have tried stopping everything for the last 15 minutes before bed time, clearing my mind. But it doesnt work, what can I do!