Depo

I was on Depo 10 years ago didnt have a period, weight fluctuated everytime I received the shot, first time gained 20lbs, next 3 mos lost weight, next shot gained, was on it for a year. Got of the shot, 10 years later i decided to get back on it, this time around had I periods sometimes twice to 3 times per month,.lasted up to 2 weeks, no sex drive, a short mood swings, and gained 40lbs in 9 mos. My question is after I finally got off the shot after 9 mos. How fertile am I ? My periods are normal again. They say it takes a while to clear your system. Im still in search for a new bc method. My concern is ,exactly how long will it take to clear your system?