How do I obtain more energy for the day?

Day starts typically around 0530, wake up. Do PT. Go to work from 0900–1700. Depends on day could be longer or rarely shorter.

Throughout the day its give or take depending on intensity of the PT that morning. Some days I am good to go I feel great. Sometimes I want to hit the gym after work, or do something after work. However, mainly run days I am drained. Just getting into work at 0900 and I feel dead already.

Lately mainly after work I have no desire,no energy. Just tired,sore and ready to sleep. But I have things to do and want to do. I am starting a class end of this month and worried this will be an issue. Among other after work activities.

Please give some ideas! I hate being tired and so lethargic after work. I am just not productive as I feel I can be.