Why do I feel tired all the time, even after I woke up? How can I improve my quality of my sleep?

This is due to sleep disorder called Obstructive Sleep Apnea 

this sleep disorder makes difficulty in breathing which makes blood oxygen desaturation & brain arousals

These arousals make you tired all the time

It is very important to get enough sleep but it's not only quantity, it's quality. The quality of sleep may be affected by many factors but I will state the most common one; breathing abnormaly. The reason why you may be feeling fatigued throughout the day can be because your body has not been oxygenised well while asleep which is probably why you also yawn frequently (if I'm correct). My advice is to try using breathing aids such as breath right before going to sleep. It is a mechanical aid that contains no medication, it just holds your nostrils in a better place for easier air flow through the nose. If that does not work you may want to try a topical nasal decongestant such as vibrocil BUT you can only use that for3 days to a max of one week otherwise you will get rebound congestion. If it's a breathing difficulty that isn't solved by simple methods, you should head to your ENT physician for a better diagnosis.

Usually feeling fatigue is connected with your food intake but it could also be health related symptom. First things first, you need to have light meal at night to allow your stomach to rest during night and not to work overtime. Before sleep people tend to use electronic devices that could actually wake them up instead oposite, so I would recomend good book and no TV in your bedroom. If you have done everything above and still feel the same I would recommend to check iron level in your blood and TSH level because hypothyroidism can cause same sympthoms. 

First of all a detailed history of  the pattern of sleep and possible disturbances has to be collected from the patient as well as from the bed partner . Any deviation from sleep heygine has to be recorded and modifed . Comorbidities like hypertension,hypothroidism,bronchial asthma has to be ruled out by relevant investigations .Other symptoms of Obstructive sleep apnea like snoring, morning headaches,lack of concentration, increased daytime sleepiness and risk asessment by berlin questionare . If found to be at increased risk a detailed plysomnography study has to be conducted and managed accordingly .

It has many reasons like Sleep Apnea ,RLS, and..... Sleep study can find the reasons...... Polysomnography.

Daytime sleepiness should be properly investigated as it might arise from many condition.

I would get expert advice as the symptom described could be related to a sleep disturbance.

It is important to avoid smoke, go to sleep regularly1-2 h after your evening meal, avoid TV.

More advice can be given after appropiate visit.

Good sleep hygiene encompasses many aspects of sleep related behavior.

In order to determine which aspects of sleep hygiene are deficient, it is recommended to seek the guidance provided by a physician trained in sleep medicine. However, there are many resources on the internet which provide good general guidelines for sleep hygiene.

A sleep study is recommended to determine if there is a sleep disorder and what form of treatment would be recommended.

the8 hours of sleep standard has been routinely to be the number of hours of sleep the most people need, however it doesn't work for everybody, and you may need to adjust a little to get it right for you, its important to dial your personal body clock so that you feel refresh and ready to tackle the day, everyday. Waking in the middle of REM can lead you feeling groogy during the day. if you wake up during the NON REM youre more likely to feel alert and attentive as the day progress