Yep, tonsil stones.
Dentist will tell you they're white blood cells or just stuck food, but they really aren't either, though they contain both.
It's like a pearl, food gets stuck and combines with bacteria from under the tongue and from your sinuses to create them. They're natural to a certain extent.
The crypts are quite deep, if you get a waterpick with the proper attachment you can stick it in the crypts and flush em out. It's when they become stuck int he crypt and keep getting bigger that they get uncomfortable and removing them becomes a pain.
It depends a LOT on the crypts. In my mouth, I only really have crypts on one side. Even if you have your tonsils removed, there is a (very) rare chance to get them. I've heard there is laser treatment to smooth the tonsils to remove the crypts (or make em shallow enough to not be an issue), and it's better than just getting the tonsils removed as they play a part in the immune system (which is probably why the stones happen in the first place).