Could have a bad o2 sensor.....maybe?, I bought a replacement for mine just have not changed it yet....They say a bad o2 sensor will set off the SES light but I'm not totally convinced it will. What year is your car?
Try disconnecting the battery for a while it might be something with the PCM.
Have you done a Seafoam? You should do that before you cance the oil, the plugs should be ok after the Seafoam since they are new.