Luckily enough I only had to work in housekeeping for three months during my course, but I feel you! I'd come home every night and just go straight to bed. Funnily enough, though I didn't even eat anything (too tired), I didn't lose any weight, I suppose I made up for it when I had a day off...
First of all: don't give up, try to find yourself a better job! (I'm currently unemployed, so I know how hard it is, but still try and go on applying.) And the second thing that basically saved me time and time again: get yourself a pair of really good shoes, they can make all the difference! Yes, money is probably short, but it is worth every penny! I know so many people whose back problems, sometimes even migraines just vanished when they got themselves good shoes. And in a job where you are running around like crazy all day you definitely need them! Especially as you are saying your feet hurt so much and your toes go numb - that is a bad sign of terrible shoes. Please get yourself better ones. Maybe you can even get some through the doctor (sorry, I still haven't got a clue how your health systems works, I only know sometimes it's possible)?
Good luck with finding a better job soon!