Yo' High plat Support main here so take my advice with a grain of salt
1.) Immediately I notice your death rate when I check your profile. Specifically - the fact that on your games that are LOSSES your death rate is very high. This leads me to believe you struggle at recovering games, or don't know how to play from behind. Focus on that. How do you recover a potentially lost game? First things first, and I know this sounds like shit advice, but try to die less, like aim for 5 deaths per game.
2.) I would encourage you to solidify your champion pool and try to main 1 specific champion. Counters don't matter as much in your elo, and mastering a champion can mean everything. Take your VERY BEST into every game.
3.) Keep an eye on how every single player is doing - always be aware of who is fed and who is feeding. This is doubly true for the 5 players on the opposing team - This leads me back to point 1 - I think you might be butting heads with the enemy when they are fed, and wind up paying the price, and giving them even more power. Pick your fights carefully and make absolutely sure you can win before you commit.
4.) Last point, Wifes waiting on me. Vision. Vision. Vision. This is really, really important as you transition from Gold to Platinum. Know where the enemy team is as often as you can. Do not fight if you can't be sure where they are. This leads to lost games.
Hope it helps brother - cheers.