Hi Emily, welcome to the forum!
Is it normal to vary in how you feel about your body? You betcha, most people have days where they are more in love with themselves than other days.
I'd be worried if it's affecting your life negatively, for instance if you start wanting to lose more weight than is healthy or if the way you see your body starts to affect the way you see yourself as a person and starts affecting you emotionally in the long term. It is also possible to actually perceive yourself as fatter than you are (many people do this to varying degree) and this can become a problem because it might affect how much weight you try to lose, or how you feel about yourself.
Personally I find it hard to accurately perceive my body weight, so I rely on external information like clothing size, weight, measurements and competent medical opinion. I also try to make sure that I focus on health and try to keep my body image separate from my self image so that I can say "yeah, I need to lose a few kg's for my health, but I'm still the same person and I'm beautiful/smart (whatever) and a nice person regardless of how fat my body is".
Regardless of how you THINK you look, you will definitely be healthier with sensible eating and a reasonable amount of exercise. If you're worried about whether your weight is actually ok, get an opinion from a GP you trust, or even a competent personal trainer/fitness/weightloss consultant. If you think maybe it's more about how you think and feel about yourself regardless of you objectively look and it's really starting to affect you, maybe think about going to see a psychologist (talk to your GP about a possible referral).
All the best with it.
35kg lost. (November 2005 - October 2006)
15kg gained again (as at October 2010).
Back to the drawing board - Let's do this thing!
"You can't change the winds, but you can change the sails"
"Reach out and take control of what lands in your lap"