2000 Kia Sephia Code P0740

I have a 2000 Kia Sephia with 100,000 miles on it. I drove it about 200 miles to a neighboring city and back again, then repeated the trip a couple of days later. The oil level was fine before the first trip. On the second trip, about 150 miles in, the car started making clicking noises and seemed to loose power. I pulled off to take a look at things and noticed that the oil was low. I added a quart, and it still looked low so I added more, eventually adding 2 quarts total. When I got back on the freeway, the car kept loosing power. My max speed eventually decreased to 25mph. I had to have a relative drive up to tow me back home. While I waited for them I finished my errands, driving around for a few hours in this state. It squeals loudly now and gets louder when given gas. Its giving a trouble code of P0740. ATF fluid looks normal in color etc. Fuel pressure is within guidelines. Intake tube looks normal. Could it be that excess oil clogged the catalytic converter and O2 sensor?