Dry rough tongue after four wisdom tooth removal and i've noticed yellow patches at the back and sides of the tongue. what could this be?

Tongue lesion: You will need to see a doctor or dentist for examination to make a specific diagnosis. This should be urgently if unwell/fevers/swallowing troubles. Here is some links to general info re tongue conditions written by dermatologists: http://www.dermnetnz.org/topics/conditions-affecting-the-tongue/

See DDS: Contact the dentist and or oral surgeon that performed the extractions for a clinical examination.