I also suffer with very low energy. My doctor checked me for diabetes and thyroid problems. I take a multivitamin, omega 3 fish oils and vit D every day. I took iron supplements for a while, as my stores were low, but now they are restored I don't need the tablets. I also make sure I drink at least 6 glasses of water a day (might not sound much, but is a huge improvement on the 0 glasses I used to drink!). I tried b12, but found it was only good for a temporary effect, so I use it if I have a big day ahead. The fluoxetine (anti depressant) has made the most difference for me. I didn't particularly think I was depressed, but I have gone from being completely unable to function in the afternoons without having a 1 or 2 hour nap, to getting a bit sleepy in the afternoons, but I'm able to work through it or just have a quick 15-30 minute nap. And as a bonus I am far less moody and stressed than I used to be!