With my spine fusing on my left side will i have lower back pain for the rest of my life?

Why fusing?: Is your spine fusing from surgery? Ankylosing spondylitis? Severe scoliosis? How old are you? These things all impact on what you may or may not be able to do. Learning little things that you can do then bring some improvement and doing more of those... Becoming aware of things you do that make it worse and avoiding those things is the underlying principle in dealing with back pain.

Maybe: If you have some instability in your spine and it's actually fusing on its own, you might actually have less pain over time as the spine becomes more stable. It's very hard to predict since there's many potential pain generators (muscle, nerve, discs, joints). See a non-surgical spine specialist first to help diagnose/treat if your pain prevents you from doing what you want.