State of Lethargy

Ever since my third son was born there has been more episodes of my being lethargic, I call it a "state of lethargy". It is natural that I should be physically tired taking care of 2 toddlers and a baby, be a wife to my husband and still have a full-time job. But I have been tired before but my work didn't suffer this much before either. I have called-in sick more than I ever had with my first 2 kids. Compounded with the physical tiredness, I also experience a mental malaise that calling-in sick has become commonplace and less guilt-ridden.***Even as I take care of my kids, when I am at the peak of this "state" I just put them in the living room, make sure they are all safe, feed them, clean them, and put Thomas DVDs all day. I don't feel motivated to play with them or read to them or teach them. And what do I do? I escape with my NookColor and read, or go to the web, or sleep. Although I may sound distracted, I am still vigilant and watchful. That's why I am not really relaxing at all because one cannot be truly relaxed when you have toddlers and babies.***I'm trying to figure out what to take or what to do to get myself out of this pit. I need to do something because I cannot afford to miss work anymore. I have been thinking about taking that energy drink 5Hour, but I don't know if its effective at all. So I really don't know what to do at this point.