birth control

Back in 2015 I was on depo for about 4 years. I was supposed to get my shot again in September but I did not. I ended up pregnant in July. Now I had my son in April this year and I was due for my depo sept 7th. I breastfeed too and I haven't gotten my period. I was just wondering do you think it's still in my system? My boyfriend and I had sex the other day. Depo was 100% effective for me when I had it before I stopped the shot.