Win lane in plat but lose in silver?

Hello, I have been playing a few normals games here and there seeing as how the season is basically over. I was wondering why I will go even or win lane in 80% of my plat games, and carry that over to the rest of the game. Unfortunately, in Silver/Bronze games I will lose lane, my excuse is that I really just need to learn the matchup better (i. e. I lost lvl 1-4 to a yas as fizz, but then won the rest of the game against him). Otherwise, is there something that I'm completely being braindead about?

tl;dr--> Title, and maybe I just need to learn the early game matchups better???