My girlfriend was on the dep vera birth controll shot for about 3-4 years?

My girlfriend was on the depovera shot for about 3-4 years. i was wondering how long will it take to fully get out of her system. ever since that shot she has had irregular periods. we have been trying to concieve since after her last shot in 2009 an have had no luck. so i wanted to know if it could be that the shot is still in her system, or should we go see a docter.