Come and see my doc, he rides too. Couple of months ago when I went to see him after crashing and injuring my hand the last thing he said when I left was don't stop riding your bicycle
For my back, he wants me to do crunches.
From what you describe, my 60 y.o. back isn't nearly as bad as yours, but hurts if I do too much sitting. Stretching out on the bike does wonders for it.
Hope you get through it ok.