I agree, see a doctor. It could also be something as simple as you being anemic. Get a good check-up. If you need to have a sleep study done, your doctor will set that up for you.
I would definitely recommend going to see a doctor who specializes in sleep medicine, preferably one that is American Academy of Sleep Medicine board certified. Based solely on the limited amount of information you provided, it is difficult to say what the problem might be. Possible diagnoses I would consider would be Hypersomnia (i.e, excessive daytime sleepiness), Idiopathic Hypersomnolence (i.e., excessive daytime sleepiness due to unknown reasons), Narcolepsy. It would also be necessary to be sure that you do not have some type of medical problem or are on a medication that is causing you to feel tired so often. I know from personal experience how frustrating it is to feel tired all of the time and as though you are never able to get enough sleep. Hang in there, things will improve and in the meantime try to be patient and go see a sleep doctor! Good luck!