What Causes Swelling With Pus Formation On The Jaw?

hi im 23 yrs old, im 5ft 2 , im 10stone, dont eat many sweets or drink sugrey drinks just water n milk n ever since i got pregnant with my son 5 yrs ago i have had 2 bad teeth, but before then they were always purfect, i had a root canal done n crown on the one n now waiting for the other one to be done its on the lower jaw 2 teeth from back, it has just for sum reason swollen n filled with pus looking stuff n the skin around it is really thin, there is no pain so should i go see a doctor tomoz or my dentist as i read sometime ago that a man died of a affection in his mouth cus it didnt get drained in time, it wernt theren last nyt but now u can see how big it is by looking at my cheek cus it is prutruding.