I played around with it for a little bit, and I found the issue, but didn't solve it.
Pretty much, the main game class sets the screen to MainMenu. MainMenu then runs its show method once then never runs its render method, and switches back to the main game class render method. Why is it doing this?
I have no idea what to do here because I've tried copying and pasting code from another screen class I made for a different project, pasting it in, then changing all the names and everything, and it still doesn't work.
EDIT: I figured out the issue. I had to add super.render(); to the main game class. Ugh, I can't believe I forgot that, and was trying to figure out the problem for a couple hours now DX. I guess that's programming though