On again, Off again sore throat? What can this be?

I was sick with viral bronchitis about 12 days ago. That mostly resolved itself in 8 days. I continue to have a sore throat, on right side only on and off again. I went to doctor's yesterday and they did a strep test as well as several blood tests (CBC, Thyroid, Platelets) All were NEGATIVE. I take Motrin for pain which helps and gargles with salt water helps pain some. Pain is usually worse after 5 pm. I usually wake up with litte to no pain. Any ideas?