Thank you for your query.
It sounds as though your sore throat
was triggered by a post nasal drip
. This can cause direct irritation and inflammation and does not need to be an infection . Also various agents , like viruses, can cause infection, which will not show on a bacterial culture. The difference you currently feel may still just be some inflammation , or sometimes small polyps (little lumps) can develop. This should resolve spontaneously with rest of your vocal cords. I trust you find this information helpful.