I have gotten progressively ill and recently have to use a wheelchair. I'm trying to get used to a chair with wheels and its hard. 
Oh no, i'm so sorry to hear that but also I'm curious to know when the first wheel chair was made
Goodness, I think they've been around since almost the beginning of time.  I saw a show that talked about seeing images of them around 525CE in Chinese art.  
Wheel chairs must be strong, what are they made of?
Now a days, they are made of metal and flexible plastic for the seating portion but mine is made of metal and more of a hard plastic because its powered; which involves batteries to help it move on its own.
Which country produces the best wheel chairs?
That definitely falls to the Chinese because they made the first ones and centuries later, still dominate the category.