I have a 2010 cobalt with 2.2 123,000 miles. 2 weeks ago my cobalt begin to misfire just a little bit. not it miss very bad when stopped at a light . so bad the motor shakes n nock. but when I drive it good. I got the two codes p0011-10 so I change the cam position sensor . it still does the same thing. plus I change the plugs 4 days go . and I change the oil putting 4 n a half quarts of oil in it . today it was only 2 quarts in it. but not oil on the ground or under the motor. it not smoking out of the pipes also.please help cause this is my gas saver. what next