pregnancy is caused by sex (obviously) and no birth control method is 100% other than sterilization and complete abstinence. so yes it is always possibility. when in doubt or changing birth control methods it is always a good idea to take a second form of birth control for the first month (like condoms).
can you get pregnant switching from depo to the pill. i was on depo for 9 months. i went off of it for 1 month then went on the pill. i had a sexual experience within the first packet of the pill is pregnancy a possibility?