I feel always tired I don't know why?

Tiredness-sleepiness. Tiredness or fatigue has many causes, including anemia, thyroid disorders, chronic infections, heart disease, depression. However, people often complain of being tired when they have difficulty staying awake or daytime sleepiness. This can be related to not getting enough time in bed, sleep apnea, poor sleep at night, narcolepy, idiopathic hypersomnia, etc. See your doctor about this.