Chances are its still a side effect of rads. Where was your cancer? Cheek, gum, tongue, base of tongue, tonsil? If your primary was in your mouth then there's a good chance you received the highest dose to your mouth. As you know it causes blisters etc. I discovered the areas where the rads beam went through took the longest to heal, and still flare up occasionally. I had one sore I was sure was a recurrence because it was so deep. It actually took cortisone to clear it up, and not your average dose. I also had another patch that would get irritated off and on.
Now the lymphadema - assuming you had a neck dissection - may take a while to subside. Once you've hit 6 months out and have had a clear scan and few clear check ups, seeing a lymphatic masseuse will help that. Numbness is very normal and semi permanent - I say this because I'm over two years out and still have numbness, it depends on what nerves where cut and how well they can regenerate
You could also have an infection so I would have it checked just to be on the safe side. Hugs!