I’d pay attention to your sleep schedule before assuming you’re just naturally a night person. If your sleep and wake times keep shifting, your body can start feeling completely out of sync during the day. What helped me was keeping the same wake-up time every day, getting outside soon after waking, and avoiding long naps. Give it a couple weeks instead of judging it after a day or two. If you're still extremely exhausted despite getting enough sleep, though, it’s worth talking to a doctor rather than just forcing yourself through it.

Could be stress or anything really. Do you take meds? How is your settle down time? How much screen time? Any ongoing conditions? All could play a role. Buuuut, there is a good podcast on sleep theory, Startalk with Neil deGrasse Tyson featuring Mattew Walker. Who has some interesting thoughts on sleep patterns. I am a cannot function until 2pm person. I function great until midnight. Then get my best sleep from 3am-8am. I have had sleep studies, hormones and vitamins checked, dropped and changed meds or caffeine and diet...nothing helped. I have chronic fatigue basically now. When I worked on my own schedule, prior to children I was soooo much more productive of a human. I even had leftover energy for hobbies, night running, painting, etc. I sadly cannot live by this sleep schedule, so just run on fumes the entire school year, as I work in a school, with school age kids of my own. So I set am alarm for 530 am, take my meds, sleep another hour, then pound coffee as well. I also have to take sleep meds at bedtime. In summer, I'm free to sleep as I need and have no need for meds. After 2 sleep specialists, two endocrinologists, and my primary told me they have no idea what my problem is, despite having it since birth, I've chalked it up to biology, and living in a Northern climate where it's dark half the year. And just roll with it as best I can.