Help! Losing Ranked

I am currently Silver 5 and have been demoted twice. When first playing ranked this season until about a couple weeks ago, I have been doing very well. I even picked random champs just for the lols and fed but still won. Suddenly, it all turned upside down. IDK why I keep losing now, even though my overall performance in recent games were great. I've tried to stick to a small champion pool, but I still lose, even though I'm using my best champions ( and ). Pls help, I don't wanna get back to Bronze.