My dad is exact same age as you and has Fibromayalga which came on after he had some serious medical conditions, this may be worth looking into. Are you against taking pain medication? I believe he takes a couple T3's when the pain really acts up. To me the side effects of meds do not outweigh being in agony!

Switching to a recumbent might ease the stress on your body, there are downsides but there is no doubt they are wayyyyy easier on your body. There are many models of high performance and touring recumbents out there. At least give it a try!