Thanks for asking the query,
Wisdom tooth is last tooth to errupt in the oral cavity and is often tilted,impacted in the jaw bone.
This area is often difficult to clean and leads to food accumulation in the region leading to redness
, inflammation of the overlying gums known as PERICORONITIS
Difficulty in mouth opening is due to pain and swelling.
I would suggest you to visit to an Oral and Maxillofacial Surgeon and get the checkup done.
Take an OPG radiograph, treatment of such tooth is extraction.
Take complete course of antibiotics and analgesics.
Maintain a good oral hygiene
,use warm saline gargles, antiseptic mouthwash gargles twice daily.
Hope this helps out.