I don't really play top lane, but the biggest thing I'd say is you need to identify when you need to Q max or E max.
Yasuo is going to just push non-stop, so maxing E would be your best idea cause you can safely get gold without giving him much ability to tower dive you (he still can, but he won't be doing it with 10 additional minions on his side). Additionally, you might consider getting a Doran's ring or Spellthiefs if E maxing to give you a little more AP damage and mana regen so you can out push him (plus free money if spellthief).
Of course, E maxing means you don't get Q stacks, but you don't want to set yourself up for ganks, which is something that's easy to do vs a Nasus trying to Q stack the 10 minions under his tower. Just Q the minions you can and stay alive.
If you really want help, go record one of your replays (or new matchs) and post it on youtube or something so we can watch it. Everything seems good based on your numbers and such, but you may be making smaller mistakes that we can't see in the end game numbers.