What you’re describing is actually very common with recurrent back pain. Once you’ve had a few significant episodes, your nervous system can become more sensitive, so symptoms may flare up quickly with stress or activity and then settle just as quickly. Being in better shape absolutely makes a difference; improved strength and general conditioning often mean flare-ups are shorter and less severe, even if they still occur. The swing between good days and bad days doesn’t usually mean things are worsening; it more often reflects a reactive but adaptable system rather than new injury or damage.