League is a lot about time. If someone is "better" then you are it is probably just because they have played longer (or made better use of their time). are you trying to learn or are you just playing half-heartily? When you die try to think of why you died, same for when you lose the game and even why you won a game as well. Learn at least one champion in each role and practice practice practice. Not many people can get to high elo jumping from Xerath mid to Nami support to Lee sin jungle, etc.
I have played for 3 years and was stuck in Silver forever. This season I went from Silver 1 to Plat 5 in less then 100 ranked games. The difference was I really started to think more about what I was doing, but even more importantly how to play with my team. Every game even if you're 15-1 you make mistakes and its all about minimizing your mistakes.
Take the losses with a grain of salt and focus on improving. GL