"Not in my job description"

I am a receptionist at an auto body repair facility. There are 9 employees. Yesterday and today, we're short 2 employees, so I get to do things that are NOT in my JOB DESCRIPTION.

I get to wash cars (some of which are standard, bad with my left knee). I have to go get lunch for the office, which includes walking through the mall, and carrying everything back to my car.
I know it doesn't sound like much, but the amount of pain involved is exceptional.

I've also decided to start myself on a high dose of Vitamin C, 500mg 4 x daily. Vitamin C aids in the production of collagen, and all the information I've found tells me that there are practically no ill effects if you take up to 2000mg per day. (Do not mistake this for medical advice, as I am in NO WAY qualified to give medical advice)

I will try to keep anyone who cares updated as to whether this helps or hinders in any way.