I had friends that did 5 hour energy and it ended up being one hour energy.
Honestley, I think I'd give someone ECA stack before I'd let them down countless things of those energy drinks. Tell him to add in more carbs, lots more.
I do factory floor work and have for 2 years, it only took me 5-6 months to adjust to my job to where I had energy at home. Then it just took me two-three weeks to adjust to REAL weight lifting and my job. I do my hardest lifting day on the weekend to rest up. It will take time to adjust to it, a good diet and sleep.
But I don't know what he has going on medically so I'm just pretending he is an average person. Hopefully it will just take time to adjust, and up his calories too. He could be tired because he is doing this all on 2500cals. A phsyically hard job, 2500cals will NEVER cut it.