18 yr. old male, very out of shape!?

I'm an 18 year old male. 5'10". 150lbs. I have very low stamina, very low energy levels, and i am always tired. I'm just not sure what the problem is. I can not even play basketball for more than 5 minutes. I can not run 100' without stopping for a breather. Does anyone have tips, heath advice or nutritinal facts?