I win lane, how do I close the game?

I have been watching quality streamers who speak their mind aloud and pickup good information. Learning about how to position as a frontliner and as a burst mage I play Syndra. I find myself winning lanes and trying to rotate around the map pushing for objectives, but when our outer turrets fall, and lanes are in the middle. No objectives are alive, what do you do? Looking for fights in the jungle doesn't work in my Elo (Gold 5) my team gets picked and it's a 4v5 soon turned into a 3v5 because going too deep to save someone is fairly common here. But lets say we get the pick, now it's 5v4 but their big cc is still alive and my comp has very little aside from me and maybe a point and click stun. Forcing it down mid doesn't result in the best and split pushing to a different lane leaves my team alone and to wander around. Getting picked once more and now falling back to regroup. It just seems hard, solo que'ing isn't easy and I find myself losing a lot even though I am strong and aim for the priority targets and focusing on my teams potential to kill. Do I need a jungler to duo with? Do I need to trio? I need advice, someone to bounce questions off of, to pick at someones brain for decision making. Thanks.