Can low-positive ANA and mild symptoms occur after short but heavy antibiotic treatment for severe staph infection from three months ago?

Unrelated. But would you kindly be more specific about what kind of symptoms, antibiotics wouldn't affect ana testing.
Positive ANA. False-positive ANA can occur after infections. Positive ANA are far more common than positive ANA due to autoimmune disease. Worried about lupus? You will want to review the diagnostic criteria for lupus http://www.lupus.org/answers/entry/lupus-diagnostic-criteria before having further tests.