Persistent sore throat?

I have had a persistent sore throat for 5 weeks now. my doctor did a strep and culture test and both came back negative. The one main issue i have is I am a mouth breather because my sinuses have been dry all winter, its hard to breathe through my nose. I am worried this could be serious like cancer. I have never had swallowing or sore throat issues this long. I have had Gerd in the past and i dont smoke and I am a moderate drinker. Any help