I've been exercising on it for about a week.
That's how every exercise routine starts out. This is because your body is not used to the strain. Fortunately, the human body adapts very easily to exercise so you just need to keep it up and not give up. In time, you'll find yourself upping the settings and staying on the machine longer and longer
There is no normal for exercising. However, why can't you go more than 5 minutes? Can't breathe? Pain in standing? bored? There may be an underlying issue you need to see a doctor for. Pushing thru it may not be the answer unless you have sound medical advise first.
build up on it.
Don't kill yourself!! Just do a little bit and leave it at that. A little bit of exercise on one of these things is pretty good because its kind of boring. So don't worry that you don't instantly turn into an athlete.
Depends .. But, as long as you keep at it, it should get better.....