In games that I'm losing when people bring up their kda I always say the same thing:
Will your x/x/x kda win the game for us?
Its different in that its a per game kda and not a player average but the sentiment is still the same. Having a great score means nothing if your entire team, besides you, is paralyzed and unable to earn gold or take objectives safely.
You need to pinpoint why you're losing per game because your behaviors are obviously having an impact if you aren't able to elevate your team when you're fed.
Are you split pushing instead of team fighting?
Are you never roaming when you have lane priority?
Are you waiting to build important threshold items (% resistance pen, grievous wounds, situational defense from GA, Zhonya's etc)?
Are you ignoring objectives?
Are you taking towers too fast or too slow?
The most important thing you must learn to do when fed is to affect the map with your lead. If you're the jungler just keep dog piling whatever lane is winning. If you're a solo laner, push and roam. If you're support coordinate with your jungler to take objectives, invade, and gank.
If you're sitting in lane with a 3/0/2 kda and not pushing down towers, taking drakes and Shelly, and not roaming you're effectively wasting your lead and letting the enemy catch up.
Map play is how you win, that's why pro games are 24/7 dog pile in their winning lanes. Get a numbers advantage, get a kill, get an objective. Spam your pings if you need to, type to your allies. If no one else will lead or at least suggest a direction to go in then you do it.