You could do a vitamin/hormone panel testing. Any toxins/radiation that you are exposing yourself on a daily basis? Check for parasites? Consume lots of animal protein/fat. Another commenter mentioned giving her husband smoothies with collagen, protein. I did the same for mine when he was doing a lot of manual labour in the past. It helped him recover physically. We used whey protein isolate, collagen peptides, BCAAs, and gelatin.