It means, the major problem might be Iron deficiency, which will raise to anemia also later.

Iron rich foods to be taken to resolve this.

Also, a basic level of calories intake also should be there in the food.

Dehydration may be also a cause, so drink plenty of water whenever possible.

See my other post on when and how to drink water a day.

Other reasons for this include:

• lack of sleep
• being stressed
• heat environment
• disease like Anemia

other tips:

• if not able to do the exercises. Try to do at least one set of all of them by taking break if needed.
• breathing through mouth will input more oxygen so more energy..so try this during workout.
• do the exercise in slow pace if feeling exhausted