1997 Mitsubishi Eclipse 1997 Eclipse burning alot of oil fr

Hello, my 1997 eclipse has bin burning oil from the tail pipe alot its got an after market exhaust on it and I recently got an oil change and it started smoking alot more the engine runs fine I had it checked buy a mechanic and he said its not the piston rings or the headgasket the comprestions good but thats all he had time to check theres no oil in the top of the engine either ( took of the spark plugs and checked if any where oil fouled ) and the check engine light whent of about 20 miles after I had the oil changed with the code p0455 large leak in evap system ( there is no catalic converter on the car btw)