It's possible to test positive for SJS and not ever develop symptoms. I have a friend who is positive for SS-A and ANA, but she only has mild rheumatoid arthritis in one finger and not SJS.
It is a ride-along disease, so you might want to ask for more testing for other AI diseases. A low ANA and positive SS-A or SS-B (do you know whether it's one or both?) don't necessarily mean Sjogren's; in fact, they don't necessarily mean anything.
Do you have dry mouth? Dry skin? Fatigue? Aches and pains in your joints? If so, it might be SJS. If not, then something else might be causing your back pain. Then again, SJS is a super weird illness and manifests in all kinds of crazy ways.
Are you scheduled for a follow-up appointment to discuss the test results? If not, can you make an appointment to talk to your doc? That's probably the best way to figure out what's going on.