It may be because of accumulation of food debris around that side due to improper cleaning of that side  and it may lead to infection. Proper oral prophylaxis is advised.

Hello , As i went through your query   The most common issue might be an existing caries .  Let me know if there is a carious tooth on the side .    That might explian the pain .  Localised periodontitis can also be your culprit. - Betadine mouthwash ,Gargle in luke warm water  2-3 times a day . - Mention if any carious tooth . - Mention if any other mobile tooth.

Any discharge from extraction site? Pain? Sinus pain? Consult specialist for concern issues.

Check if any other tooth is not detoriated ..which might give you bad breath Surgery site shld also not be infected ...if there is infection it will give you bad smell

Start rinsing with warm salt water and a mouthwash like betadine. May be the area is attracting food so foul smell. If there is pain or if you feel pus oozing out then get a xray done.

Do you have pain?