Unfortunately if the docs haven't found anything up to now, something significant would have to happen for more tests to be ordered. Although BOT cancer per se is difficult to find, by now it would have certainly been discovered, in my opinion. Although not a fan of CT scans, after diagnosis I went back to a panoramic dental X-ray and could clearly see one of my lymph does that had cancer.
I don't know of many if any at all that had severe pain without an obvious problem that was seen on scans. I also don't know many that had any pain for that matter. I could not turn my head because of the tumor in my throat. It was not painful at all.
If you believe something and insist that others should pursue no matter what if they believe too is something that you need to come to grips with. Many of us, myself included, preferred the "prove it" method with cancer being the last thing we would accept until there was concrete proof. To assume it is cancer first and then seek out proof to support that "feeling" is almost counterproductive. Get back to life and if you feel you must, pursue it every 90 days. Something will be found eventually if it is cancer and you would have an extra 89 days of rest between visits.
I have met people that incessantly demand a doctor diagnose ALS. I will never understand why a person's mind would go to such a dark place, convince the body something is wrong and then seek out evidence to support the myth. It is a sign that you really want something bad to happen. Maybe get a dog or cat if you need the attention. Clogging up medical facilities after many doctors don't agree only takes care away from others that may need it NOW. Find a facility like a free clinic that will take your money and be able to use it. If you like I will make the diagnosis provided you will donate any fees to OCF.
I hope for the best for both of you but I would have to change the advice to go out and find a hobby or interest to keep the mind busy...except for 1-2 days a month while you keep pursuing your gut feel.