I agrre with a thorough medical checkup as listed above. My first stop would be an overnight sleep study. Daytime sleepiness can be a result of several things, but quite often it is because ones sleep is not restorative. Please do use extreme caution in anything requiring alertness. If you should happen to have a sleep disorder you will quite likely experience progressively worsening symptoms, and what you are describing could accompany microsleeps. Narcolepsy? Probably not, but if it is determined you have no medical or sleep disorder explanation for you symptoms, then an evaluation for narcolepsy might be considered. But they'll want to rule out any other possible cause first.
Family doctors seem to be very bad at diagnosing the cause of fatigue. Are you overweight? Do you snore? How old are you? Are you anemic? Do you need B12 supplements? Do you have asthma? In any event, ask your doctor for a blood test, and have him or his nurse explain each and every item to you. Ask them to check both your estrogen and testosterone levels. Make sure your thyroid is functioning correctly. Allergies, food or otherwise, could cause your problems. You have to be aggressive with your doctor, and challenge him to keep working on the problem, or change doctors until you find one who can make you well. They now have a TV show with rare diseases, hopefully you have a problem that is easy to fix. I would suggest a vegan diet, planned with your doctors help, to make sure it is balanced. Eliminate all alcohol as this relaxes your throat muscles and worsens sleep apnea. Eliminate all caffeine. Sleep on your side, not your back. Basically you will have to use trial and error until you find the solution. It is up to you. Chronic fatigue is a cop-out by the doctor who could not find the root cause of your problems.