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'.