Wisdom tooth is the last tooth to erupt in the oral cavity and often its eruption is associated with symptoms like pain and discomfort in eating , difficulty in opening mouth , swelling in the jaws and sometimes infection.
wisdom teeth are often tilted in position and impacted in the bone , gums overlying the tooth usually undergoes inflammation known as pericoronitis
swollen sac like structure you have mentioned is may be the pericoronal flap or the infection arising from wisdom tooth.
i would suggest you to go for symptomatic treatment at home like gargling with lukewarm saline water or antiseptic mouthwash like chlorhexidine
consult a dentist
and get the examination done and if needed get the tooth extracted surgically this will subside your swelling as well.
i hope this helps ,