It may or may not be useful to you, but when I am constantly tired I've found it can come from one of two things: not eating enough calories, or I need to take vitamin B12 supplements.
I'm probably tired from eating too much calories. Vit B doesn't help a lot. But I changed my lifestyle recently from almost constant sitting to almost constant standing, a lot more movement, less calories, lost a lot of weight (still a lot to go) and it helped, but not that much. I tried a lot of supplements along the way. Looks like I'm destined to be the pidgeon...