Work and fatigue

I just started a part time job yesterday and the fatigue is literally kicking my butt. It's not a lot of physical work at all but I'm just constantly finding myself fighting this tiredness. Not to add the headaches I'm starting to get! I want to know how you mommy's do it to get thru the day? I'm only working 5 hours a day and it seems like a lot. I do have fibromyalgia but the fatigue wasn't this bad before pregnancy. I just need any suggestions on coping and getting thru. I really appreciate it