Dear Janegrant:
First, I'm so sorry to hear how difficult it is for you and that the children are such jerks about it. I know, sometimes it is the way that they deal with a sick parent, but they are adults and they need to step up. It seems that they won't though and I would like to throw out some suggestions:
First, I agree that he needs to see a pain doc. I have a friend who has had stage 4 breast cancer for 17 years. She's had many different types of treatment and they have given her a long life, however, the side effects have been debilitating at times. Most often though, they go away. So, seing a pain doc might shed some light on what is going on. I would first talk to your oncologist, he may be able to pinpoint the problem right away.
Next, you need a break. You will have to search, but there are many sitter services, some are paid on a sliding scale, who will come and stay with him so you can get away. There are even overnight services. Google them in your area. It would be great if you could get away for a couple of days with a friend or family member. Maybe his siblings could care for him for a couple of days. It is imperative that you get some rest so you can continue to care for him. You are right, you are getting sick. It is inevitible with the stress you are under.
I wish I had a silver bullet, but each situation will be worked out in it's own way and time. Feel free to contact me if you need to vent. I'm a good listener.
If you have a church home, call your minister and set up a session with him/her. Check with your cancer center, sometimes they have connections with counselling, support groups, etc.
Many Blessings,
jan