The "pills" are an indication of how much weight people have lost and how much they have left to lose. They are color coded based on how close they are to their goal. I.E. You change colors once you are halfway there and then you change again when you've met it. I don't know the exact color breakdown though.

Fatsecret is pretty inflexible when it comes to getting the account to backdate your weight, chances are unless you want to open a new account, you're stuck with the starting weight it's giving you.