Lose every ranked game

I don't understand. In my last 20 games i've won 3, like it's not a 1 day losing streak or a couple of days. It's over and over I lose. My MMR went from Silver 3 to Bronze 5. For example last game I went 7/0 in the first 20 mins and then we still lost. I just don't understand how I'm supposed to win these ranked games, any advice?!?! And I understand I'm not that good, as I am in Bronze but what can I do to help my chances.