The thing is there's a big difference between ranked and normal games. Normal games are a lot about trying to learn new matchups and champions and someone might be less familiar with their champion than you. So if it feels like you're dying too much in lane in ranked, it's because people know the matchup and how to punish you while you're stacking.
The other big difference is nobody in normals cares about macroplay, Nasus' biggest weakness.
So if you're wondering what macroplay is, it's knowing how to play the map to your advantage. In Nasus' case, while you're weak and unable to group up for fights they should go for objectives and take towers. If they do that, your entire team falls behind and you're not strong enough to make up for how ahead their team is.
Also, I looked at your stats, Dark Harvest is not a good rune for Nasus because he has difficulty killing things, so it doesn't help him to stack it. You'll probably want something that's stronger on him earlier in the game.
https://lolalytics.com/ranked/worldwide/platinum/plus/champion/Nasus/Top/
If you look through this page you can see that the two most common runes are Conqueror and Grasp of the Undying. The most common secondary is the Inspiration tree for the cooldown reduction. I think you should go for Grasp and the CDR rune in the inspiration tree, then Magical Footwear in melee matchups and the Biscuit Delivery mastery in ranged matchups. Also, make sure your stat shards reflect the matchup you're going against (armor into champions that deal physical damage, and MR into mages).
