Constant sleepiness

So.. I am planning on speaking with my doctor soon. I have set up an appointment for a check up.

But for a long time now I experience just extreme exhaustion from literally nothing. I am typically getting enough sleep at night but during the day I get very tired. I’ve changed my diet to a more healthy path so I am staying away from junk food and sodas. I still have snacks but healthier options. When I feel awake I feel fantastic. But it’s only a matter of a few hours that I feel very tired and want to sleep.

Sometimes when I have the day off I take a nap for a few hours and then feel great! But a few hours later I am sleepy once again. Does anyone have any insight on what this could be? Did I change my diet to quickly? I’m not over exerting myself with tasks and I feel bad for feeling so tired. Thank you.