2004 Pontiac Grand Am Question: Code P0420 plus Check Oil Light

My 2004 Pontiac Grand AM GT has a P0420 code plus change oil light on. The Oil light came on first, and a day later, the check engine light came on. I checked the code and it was P0420 code, which is a catalyst efficiency low-bank which could deal with a bad catalytic converter or an engine misfire, large vacuum leak, or engine oil leakage into exhaust value guide. It does smell like burning oil when I open the hood. The oil was changed in the last month. What should I do? Has anyone had this problem before?