Diagnosed with Pericarditis - on Prednisone. Started @ 40 mg, reduced 10 mg/week, reduced to 10 mg?

... and symptoms came back. Back on 20 mg with minimal symptoms - how long is it safe to be on 15-20 mg? Have some work/personal commitments for next 3 months keeping me from taking possible next step (pericardectomy, ??? ) Have had no weight gain, moon face, etc. have occasional leg camps @ night