Hello,
There could be multiple reasons for the discomfort.
1) It could be referred pain from the still healing from the extraction site. Bone healing takes at least 3 months, there may be a little discomfort now and then.
2) It could be due to decay in the 2nd molar tooth that is causing the discomfort. Sometimes the decay is not visible from the top, usually the decay starts between the 2nd molar and the wisdom tooth.
3) It could be because of the sensitivity in the 2nd molar tooth. In case of horizontal wisdom tooth extraction, there is usually bone loss causing a part of the 2nd molar tooth to be exposed, causing sensitivity.
Next Steps
Check with your dentist and OPG/CBCT to guide you to a definitive diagnosis.
Health Tips
Use lukewarm salt water rinses