I constantly feel tired all the time. I dont know why?

Hows your diet?

Are you getting enough sleep?

If all other factors seem okay and under control you should pay your doctor a visit. Fatigue can be a symptom of a lot of things. So go get it checked out, I'm sure its nothing major and you'll be bouncing off the walls again sometime soon (:

I agree, focus on your diet and exercise as well. And if nothing works, then see your doctor and get some blood work done. You might be anemic. You also might be depressed.

You're not getting enough sleep, or whatever your doing is exhausting you. Probably energy drinks, caffeine would help. Or a safe resort just doing more exercise.

Get a medical checkup to find out why.

There are many possible reasons. Some of them are behavioral and some are medical.

If you don't get enough sleep for one reason or another, then this could be a reason for you feeling tired. But it can also be some illness, or anemia, or a vitamin deficiency.

Increase your iron intake. Green leafy vegetables and liver are a good source.