Welcome to the forum,
The area surrounding the wisdom tooth is difficult to clean and often invites bacterial infection leading inflammation, swelling of the surrounding tissues known as Pericoronitis
. Pus formation can be due to food accumulation.
Best treatment for pericoronitis is extraction of wisdom tooth, but it cannot be done right now.
As you have mentioned that you are 8 months pregnant, so extra care should be taken, i would suggest you to take a course of antibiotics consulting to your OBGYN
You can plan for the removal of the tooth after the delivary of your child.
Till then take lukewarm saline rinses 3-4 times daily to give a soothing effect,
take antiseptic mouthwash rinses twice daily to prevent superinfection
Maintain a very good oral hygiene
Avoid eating from the affected side.