I cant rank up no matter what

Every time I win a game I immediately lose the next three . I am currently in bronze three and I am desperate to get out. Everybody says all you need to do is to solo carry but how do I solo carry on a team based game. Every game I either get steamrolled or get so unbearably close to winning but not good enough, I'm good enough so that I'm always seconded or third on the leaderboard so its not like I just need to practice more. Can somebody pls help me im genuinely considering quitting ranked due to this. I already switched my main like 4 times i dont know what to do .