Poor energy levels usually indicate you are not eating right.  You need the right foods to fuel your workout.  Check you are getting the correct carbs before exercise.

I could be your not getting enough sleep or calories.

You need to make sure your using progresive overload when your working out, you have probably been doing to much on your body its catching up on you, you need time for your body to rest aswell, so your body and musccels have enough time to replemish and repair any damage to it, outherwise you will just cause indury on yourself, make sure your warming up your muscels and getting your heart pummping before you exersize it makes them more awake and flexable that avoids indury and pain, also after your workout you do a cool down, this determains your pain you will feel later on, flex your muscels out do a light exersize after, instead of compleatly stopping, sorry for lecture haha this will all help and aid pain
From a PE teacher :)