Too tired to have sex

Hi, I've been around reading for a while and this is ky first post. I'm 24 and love my husband (28) he is everything a man could be and I Trust him to lead me but, for the past 2 weeks I've had kind of a headache. I'm a teacher and worked part time 13:00-18:15 wich was great but not as good pay as I would like , we share the bills, the rest of our finances are apart but I like doing things for him since I make the most money. It all started when I got a chance to double shift we talked over and he told me I should do It, so I'm working from 7:00 to 12:00 and then at other school 13:00 to 18:15. The first school takes about one hour and a half to get there so I wake up at 4:30 everyday and come home at 20:00 because of extra hours I'm obligated to do, so of course when I come home I still need to cook and clean and all of the house work so when I'm done, around 22:30, 23:00 and he wants to have sex I'm completly and fully exausted. I haven't deny it yet because I want to be good to him but I don't feel any pleasure, I just think about sleeping. At the weekends I'm back to normal but from monday to Friday I just want to drop dead in my bed. I don't know what to do as I'm not sure I want to keep doing this, sometimes when I'm under him I have to fight myself just to stay awake. Any advices? Ps: Sorry for the broken English