I am always tired. Why is this?

Many things. Dehydration, common fatigue, anemia, thyroid disease, stress, depression, and many many other things. See doctor if concerned and affecting your daily life activities.
Many possibilities. There are innumerable medical, nutritional and emotional conditions that include being tired as a symptom. These range from simple issues to those far more complex. A good checkup and blood testing would be a good starting point.

Related Questions

I urinate every 30 minutes and I am always tired...Why?

Get checked. The symptoms you describe could be due to a urinary tract infection or diabetes. Simple testing can easily be done to find out. Good luck and hope you're feeling better soon.

Is there a reason why I am always tired and why is my heart always beating fast?

? Anemia. Anemia (low red blood cell count) could cause both of those symptoms. It can be easily checked in most doctor's offices.