Hi Jacob,
Definitely not normal, I'm afraid. Lithium Ion batteries can swell when the chemical reaction that happens when you charge and discharge the battery no longer works correctly, which can generate gas, causing the plastic casing/coating on the battery to swell up.
This can actually be a dangerous situation, in the worst case the battery can actually catch fire - remember the Galaxy Note 7?
You need to take care of this ASAP, my friend. I hate to tell you, but you're in the market for a new battery now. Here's an iFixit Wiki article on swollen batteries that will give you more information.
What to do with a swollen battery - iFixit
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