I have been off the Depo-Provera shots since aug 2010... And have not gotten pregnant yet. I'm 20 years old. Should I worry?

Seek answers. Depo Provera (medroxyprogesterone) can remain in your system longer than the every 3 month interval you have to get the shot. That being said, you are now16 months without birth control. 85% of couples will be pregnant in 12 months without birth control. You should see your obgyn to discuss next possible steps and look for any other potential issues you may need to overcome to get pregnant.
No. I would not worry yet. You should see an obgyn or fertility specialist to see if the depo is still having an effect on your body. Sometimes it can suppress your body's hormones even more than 1 year.