I think the reason that you do not have enough strength in the morning is probably because you did not get enough sleep at night. There is a clear connection between sleep, exercise and tiredness! Most teens need 9 to 10 hours of sleep a night. If you don't get enough sleep, you may have less strength and stamina while you are exercising, you enjoy exercising less, and you are less motivated.

The other factor that influences how active you feel in the morning or during the day is your food (energy) intake. Food (especially carbohydrates and fat) provides your muscles with the energy they need to exercise. Muscles are very complicated structures, which contain some fibers that carry their own fuel supply in the form of a glucose polymer called glycogen and the more glycogen you have stored in the muscle the better you can work out. This type is responsible for rapid, short-duration strength exercises like sprinting. Other fibers depend heavily on fuel and oxygen supplied by the bloodstream while you are doing the exercise. Long-term endurance exercises such as running, cycling, aerobics, and weight training rely primarily on glycogen and oxygen.

So if you get enough sleep, have a proper diet (this means eating a nutritious breakfast in the morning) and exercise regularly, then you should not feel tired and weak in the morning.