If it is eating oil heavily, than piston rings are usually at fault. I would perform a couple diagnostic tests on it if I were you. A compression test to see if compression is un-even or just dropped. Usually when compression is low in only two cylinders adjacent to eachother, that is a sign off head gasket failure. After the compression test, do a cylinder leakage test. This is done with a pressure gauge and shop air. This test is a little more complicated, so I recommend a shop perform this test for you. Also check the "no brainer" stuff, like your drain plug, oil filter, pan...see if its loose, or if the pan is cracked. Leaving the car parked on a level ground with cardboard underneath it and let it run at 2000rpm for about 3 minutes, than let it sit for about two hours. Check cardboard for oil leaks. If nothing, than your problem is internal.