I concur that you need to discuss this fatigue with your doctor; get some basic lab work done to rule out culprits like thyroid disorders, electrolyte imbalances, and anemia; and pursue a sleep study WITH MLST** if all that comes back negative. I highlight the MSLT portion, as this is necessary in addition to a basic polysomnogram when trying to diagnose daytime sleepiness such as Narcolepsy or Idiopathic Hypersomnia.
Expensive but a professional sleep study should tell you what is the matter, or at least establish what is missing, e.g., REM sleep time. Not all hours of sleep are equal in terms of getting rest.
Do you week solid when asleep, or do you often wake up...maybe feel shot of breath or have a high heart rate? This could suggest Sleep Apnea.. which would be found in a sleep study.