Lots of things are now invisible!

When I log into Minecraft, instead of seeing the usual gray boxes with words in them, I just see the words, and I can't see my skin either, just my moniker. Inside a world, I can't see my hotbar, only the items in it. I can't see my health of hunger bars, and I can only see certain mobs (for example, I see Drowneds, but only the outlines of chickens or pigs). I can't see players either, only their outlines, their usernames, and sometimes the armour or items they're holding. Help?