What Causes Pregnancy Symptoms While On Depo Shot?

Hi i went for my depo shot on the 20th February and i was going to be visiting my boyfreind the following day 21 Feb, i had my period from 13th Feb and ended on the 15th Feb i have always had irregular periods since 2012 when i started depo, and i am now experiencing pregnancy symptoms like tender breast and swollen feet is it possible that i might be pregnant?