Can an abcessed tooth lead to pressure in the head?

Yes: An abscess is fluid and pus that is building up in a confined space. By definition, an abscess causes pressure. Sometimes the fluid finds the path of least resistance and drains out of the abscess, at which point the pressure will diminish. But drainage doesn't indicate that the problem is solved. You should see a dentist or physician to resolve this abscess for you.

Yes: Abscess is an infection that can spread.