lepper

I think you've got to look at the scale with a +/- 4 pounds range. I found this article. It seems to explain it pretty well: http://www.ehow.com/facts_5007466_what-normal-weight-fluctuation.html. It looks like you are already thin. Keep up all the exercise and eating well and don't worry so much about the scale.

I'm no expert, but I would say your time is more important and your distance was close enough given your height. If I were you, I would also use a heart rate monitor.