What Causes Sore Throat And Sinus Infection?

I have had a sore throat on and off for 2/3 months together with mild sinus problems. Its on the right hand side near to where I have had a major filling on my back tooth. I am 60 years of age and ex smoker, gave up about 8years ago. My GP gave me nasal spray but would not refer me to ENT. Should I go back to my dentist or get second opinion as my GP just thinks its sinus problems.