I was involved with a man who was in his mid 70s and he suffered from lower back pain, plus he was on a good deal of medication. His libido was affected by this... but, we noticed that after several chiropractic manipulations along with acupuncture that libido began to perk up (no pun intended).
Narcotics can absolutely effect many aspects of your health, including sexual drive. Also, as we age our sexual drive decreases. The use of Viagra is for men only, but I recommend that you talk with your physician regarding your concern. I'm sure your health will be re-evaluated, before your physician will be able to prescribe any further medication. Many people your age have a very satisfying sexual life, but please go and have a second opinion....it's fixable....good luck! Judy
Talk to your pain doc about drugs that could mitigate the effects of the narcotics. It's possible that the narcotics are affecting chemical pathways in your brain that are suppressing the chemicals you need to maintain desire (serotonin, or whatever).
There are studies under way to see if Viagra works in NORMAL women to help boost desire. It's possible V could help you the same way.
I would also look at other issues in the marriage or what else is going on with you. have the 2 of you seen a sex therapist about your issue?
Also you should post this on the pain management forum (if there is one here). They might be able to help you too.