Hi Julie,
In my own experience, my first OS started saying it was back problems when the hip was failing. Actually, this happened to me both before my hip was recognized as needing to be replaced, and after the Hip replacement wasn't so satisfactory. Don't expect the OS who did your hip to say "Oops, I screwed up!" Get the rep of someone very good and get a second opinion. The most non-invasive thing you can do to check your back is get a EMG (electromylogram) which you did. This will tell you if you have problems with any of your back nerve roots. Stay away from cortisone injections as tests - it breaks down cartilage. None of us need more of that! I've allowed them to give me way too much over the years, and most of the time it didn't work. There's that first good one, but afterwards ... :P
What works for me is pacing myself. After an active day, take a slow one. Gabapentin helps with my nerve pain better than other meds. It doesn't get rid of the pain, but dulls it. True sciatica (for me) caused pain in my foot first.
There's the psoas muscle too. Sometimes it impinges. Sometimes they use that as an excuse for a less-than-successful hip. Jo's right about the Piriforus too. Tricky ****** to get to. Massage is great and glad it's working for you
I have trocanter bursitis (I'm told) too, but it's more a symptom than a cause. Try rest and ice and see if that helps, and I mean staying down and icing whenever you don't have to be on your feet.
In the meanwhile, look for that new OS. I think they like to play Patient Hot Potato, or is that Already Paid And Tired of Hearing You (APATHY).