While there are many possible causes of extreme daytime sleepiness including dietary deficiencies, depression,
diabetes, anemia, or
thyroid problems, chronic daytime fatigue can very likely be caused by a sleep disorder.. it also depends since when you are having this . Ideally it would be better to get a medical checkup first and if necessary talk to a counsellor about any possible disturbances in your mind
Next Steps
take a medical checkup