iPhone SE randomly drops battery.

I have an iPhone SE generation 1. I've been having this problem for a few days now.

I'll enter an app, it'll glitch and be extremely laggy for around 5-15 minutes, I'll have to click the power button dozens of times, it'll shut down and when I turn it back on it's 0%.

I went from 70-90% to 0% with this, it's extremely annoying. It may be because I have a swollen battery (I think) but I don't know, this is very frustrating. Please help.