1999 SE check engine light and oil light

I have a 1999 Grand Prix SE. At 5:00am, the car was fine; at 7:00am, I started it and felt something wrong. The car ran, but it felt like it was 'missing'. While driving, the 'miss' could be felt in the steering wheel and in the permformance; it was as if all cylinders weren't firing, or maybe a fuel injector had dirt stuck in it. At 6:00pm, it ran fine, but the check engine light was still on. I'm going to check the gas cap and see if there are any vacuum lines that are off, but what else can it be? I know, there are hundreds of things, but can you narrow it down? Can I try and reset the light so it goes off? Also, the change oil soon light has been on for a year, even though I change the oil every 3,000-5,000 miles and follow the instructions of - turn key on (but do not start car) and push the gas pedal down 3 times within 5 seconds. It used to work, but now I can't get it to go off. Any ideas on that one?

Thanks in advance.

Joe