I noticed today that my embouchure is tight. My teacher had been working with me to help relax it, but today after practicing for a while it tightened again. I do use flute whistling, whisper tones , whatever you want to call it , but does anyone have any additional exercises, or ways to relax the embouchure?

Try this:
http://www.youtube.com/watch?v=VQg0vScnQ8E