How do i get my mom to back off?

for the last few months of the school year, i have put on some pounds due to stress from SATS, finals, and projects. my mom keeps badgering me about losing weight and exercising more, but i really don't have the time. I exercise at least an hour a day, but she still is bugging me about it. i promised her (and myself) that after finals i would exervise more adn lose weight, but she won't listen!!! how should i deal with her?