Is changing Invisalign aligners every week too soon?

I've been on Invisalign for six months now and was originally instructed to wear my aligners for two weeks. Now, my orthodontist instructed me to change my aligners every week (and I'm not using Acceledent). Is that normal? I've read that changing them too quickly can cause damage and I don't want to my teeth to end up falling out or something.