Hi J,
I don't know about the cetuximab, Martin never had chemo. But i know that he had persistant earache and a headache that went from the ear to the top of the head.
The pain is now much less frequent. Our consultant was not too concerned. he said it is normal to feel ear and head pain. They had to sever some nerves and moved and touched muscles. The nerves and veins and everything are trying to heal and grow back and it does hurt. he did send martin for a scan, but saw nothing.
Maybe you should ask your Mum's ENT team. they might also say it is normal, but might suggest some checks just to make sure.
All the best.