Drink more water, eat healthy, don't sleep for nine hours (aim for 7-8 hours), eat a good breakfast at the start of the day, exercise. Get fresh air, even if it's just through opening a window. Finally, socialise vocally. That includes talking on the phone and in person and of course any other way, so long as you socialise vocally then I find you don't get so tired so quickly. But yeah, do all of those many things or at least some of them and hopefully things will pick up.