Why can't I win? (Ex-Plat)

So, at the end of Season 4 I ended up Platinum. I basically was mid-plat range for the last quarter of Season 4. After provisionals, I was placed in Platinum IV, which is basically where I ended at the end of the season (When it didn't matter anymore) My first 20 or so games afterwards were regular. I was where I belonged. I was winning a couple, losing a couple. I strictly remember a 52% winrate, which means I deserve to be there. No higher, no less. All of a sudden, I just dropped. Like, 10 losses in a row drop. I am finding myself teetering on being demoted to Gold 5. I don't understand what I did wrong. Being an ex-plat player, I played against some pretty ok players. But now that I am playing with these high silver/low gold players. I feel that I am a giant surrounded by ants. My lane opponent has no idea what he's doing, so I just roam/kill him, and then I somehow just lose the game. If someone could help me that'd be greatly appreciated as I obviously suck donger if I can't beat these Silvers as a Platinum player. Take a look at the drops in ELO in the graph.

TL;DR I used to be plat 3, now I am consistently losing to Silver/Gold players with a 52 Wins and 73 Losses ratio. About to be demoted to Gold 5