Sorry to hear that you are having a tough time. I know that fatigue is hard and must be frustrating let alone a hardship to your health physically and mentally. Mentally I mean in the sense of that it is harder to deal with things when you are so tired.
I really cannot offer any advice that is a given. Have you gone to a doctor and talked with them about your fatigue? Another option is going to a health food store and seeing if they have any suggestions. There are tonics and food supplements that might help you.
Try not to be too hard on yourself. I would try and get some input from a doctor if you can. It is always good to know that nothing serious is going on. It helps me to know what is going on, my stress level goes down. As Ksp suggested, look at what is going on in your life, sometimes problems sneak up on us even though we think we have it covered IMO.
Take you naps. Your body is telling you something and you need at least that rest.
Hang in there, take care of your babies as you are. You sound like a wonderful, loving mother.
Peace and love, Janet
"Compassion can help heal our World"