3 months post rads is a worrying time. You don't have the clear results from the PET, you are still suffering the same sore throat you had before treatment, it doesn't feel like anything has changed. With the surgery on the lymph nodes the repair process is even slower. But all that is completely normal and the phase does pass. A false positive on the first PET is not uncommon with all the inflammation going on.

Recovery is not linear, and there are setbacks along the way. New pain like any change in symptoms should be reported to and managed by the doctors, but don't be surprised or unduly worried when there are bumps in the road.