I cant relax till I finish my work. How can I change this?

Even if I try to set away a couple hours of doing nothing, I still feel nervous and guilty about all the work I could be doing. Its like I can't think my brain is buzzing. Then my stress piles up. It doesn't help that It takes forever for me to finish stuff. And then I feel lazy. I usually go home and set away time for a couple hours, then stay up late to do homework. So its not like setting time away really helps me be productive. But I like to relax, and I don't know what else to do.