What is this tiny dark dot on my tooth that hurts when i push down on it?

Decay ?: That's only a guess... you'll need to be examined by a local dentist for a proper diagnosis. These types of problems don't really get better on their own, so the sooner you go to be seen the better you will feel.

Hole: A hole in a tooth is a cavity, probably much larger under the enamel. If you can see damage, the cavity is probably extensive. Pressure sensitivity may indicate abscess (collection of pus) formation. You need to see a Dentist immediately.