Is there a spell for carrying more weight in Skyrim?

There's no such spell in Skyrim.

You can carry more weight by:

  • Wearing items with the Fortify Carry Weight enchantment
  • Drinking a potion of Fortify Carry Weight
  • Adding points to Stamina when you level up
  • Giving some stuff to your hireling
  • Climbing onto a horse
  • Using The Steed Stone, allows you to carry +100.
  • The Extra Pockets perk, which is part of the Pickpocket skill, also allows you to carry +100.

In the vanilla game, no. With mods, yes:

  • Carry Weight Spells
  • Feather Spells
  • Ancient Spells - Morrowind and Oblivion Spells

Note: In older TES games like Morrowind and Oblivion, the 'fortify carry weight' spell was named 'Feather'.