Janet is right that we're not qualified to diagnose you, and especially not on the internet... If in doubt, consult your doctor!
But "back pain" is a wide term: I have back/shoulder/neck pain almost constantly now, since I started training 3 or more times a week. But I know it's just muscle pain from all the tensing required when rolling and falling. Nothing a good massage won't fix (especially when the massage guy comes to your workplace
I like the idea with rolling tennis balls along the spine. I intuitively tried to do something similar lying with my fists under my upper back. It helps.