Catalytic converter and oil light?

An oil light doesn't usually mean the oil is low. It means the oil pressure is low which is a severe condition. However, when those lights come on -- 99% of the time it's because the pressure sensor switch has worn out. For most cars they are cheap and easy to fix.
Don't just add oil. Check the level first. Engine off, car level, and don't do it right after you turn it off. Let it sit for a few minutes so the oil can drip back into the pan (having been circulating through the engine).

The catalytic converter is a section of the exhaust that filters some of the gases. They don't usually cause any trouble. When they get old they can rust and develop holes. Sometimes the ceramic material inside can break loose and make noise, even then it's not necessarily a problem, just irritating.
In some cases they can clog with oily exhaust and cause the engine to run poorly and usually hot.

The lube boy that changed your oil evidently did something wrong if you're losing oil that fast. Have them check to see if the old oil filter gasket was left on the motor. That would cause oil loss.

The oil situation and check engine light have different priorities right now. You are losing oil and you must fix that FIRST. Sounds like a double gasketed oil filter to me.

Did you check the oil dipstick before adding two quarts? If it's 2 quarts low right after getting an oil change, then take it right back to the place that changed it. They didn't tighten the drain plug or the filter.

If you took it the mechanic and he said its the catalytic converter and you didn't know what that meant, why in the world didn't you just ASK him.

None of your statement makes sense. There's got to be lots of missing info. Take it back to the mechanic and ask him to explain.