Hi,
Ive had back trouble too, and lots of it. After talking to so many people with back trouble, I ve concluded that people have relatively unique problems with their backs, that is one persons solution isnt necessarily going to work for somene else.
I do know that one of the very few things that helped me was to lie on my belly on the floor,simultaneously lift both your feet and arms , raising your upper chest a bit, and your upper legs should bend back, then and extend your legs and arms and repeat this. Do not push this to extremes and if you get a sharp pain while doing it, stop. Maybe three sets of seven to begin with, the first day it hurt worse, but overnight it helped. This strenghens the muscles in the back and belly.
Another thing is staying out of chairs, most chairs hurt me, stay on the feet, or lay down is what I do unless I can find a chair that reclines very seriously, say forty five degrees. No more straight chairs for me for any extended period, more than ten mins for the last ten yrs, yet there are people that say straight chairs are good for their bad back. If muscle relaxers help, then you prolly have mostly muscle problems, if not, maybe its pinched nerve.
Hopefully you dont develop leg pain, that is definitely worse and the lower it goes in the leg, the worse the problem is. If it were me, I would consider giving up the riding for this year. No one ever wants to hear that, but thats what I would consider while you get your health back.