Dull ache in back top two teeth and slight swelling. Already had wisdom teeth out and everything was clear at my last checkup. Anything to worry about?

Dull ache. Your symptoms indicate an infection. This needs to be treated or it will get worse. Things have changes since your last checkup. See your dentist ASAP.
Re-evaluation. How long ago was your last check up? Even if it was last week, something is different today to cause that swelling. A trapped food particle? A loose filling? A piece of calculus? An undetected problem? Have your dentist take a look....
See your dentist. to drain the dental abscess. If not treated, a serious dental abscess can eventually kill. The infection may spread to your jaw, cheeks, sinus and to other areas of your head and neck. See any dentist for examination, x-rays and treatment. Remember, the only way to cure a dental abscess is with dental treatment.