Ok all. You knew it was coming...so now I chime in. I apologize in advance if I step on toes...I honestly don't mean to.
First of all, wait on the injections. Several huge studies have just come out that says they are no better than regular physical therapy for your back, especially for chronic issues. I do sometimes recommend them to my patients, but ONLY if what we are doing is not helping.
Secondly, go to physio and make sure your PT actually does hands on treatment. No hot packs, no ultrasound, no electrical stuff...it's all garbage. Yes people will swear it helped them, but there are plenty of randomized controlled trials out there that show they are no better than placebo. You will do just as well sitting on the couch watching Oprah. Will people here swear that's what fixed them? Yep. But that's correlation, not cause-effect - they would have gotten just as better without it. And why not try, you ask? Because it takes time and attention away from the interventions we know to be effective (joint mobilization and manipulations, and very specific exercise).
People here do a great job of telling you the exercises they do to get better - that's great. But every back is a bit different...and while walking may have felt great for one group of people with "herniated discs," it may completely aggravate another group whose MRIs look identical.
Since you are going to a physio - listen to him/her, and make sure the PT is a good one (there is a boatload of crappy treatments for back pain out there).
Do NOT NOT NOT ever wear a back brace. Our bodies are inherently lazy and if a muscle doesn't have to work it won't. When you wear a brace, all the core muscles of your back and your abdomen turn off. Completely. So every time you take it off your body has to re-establish all those connections between your brain and the core (which is a tenuous connection for most of us)...and there is a strong likelihood that it won't turn back on sufficiently. There is actually a great deal of literature about construction workers who wear braces while lifting heavy objects - their rate of back injury is actually higher than their counterparts.
As for backpacking - everyone here who mentioned dropping pack weight is right. Pack weight, body weight...all of it. The less downward forces through your spine the better it will feel and the easier it will be to control your core.
Good luck mate....