1995 Lexus ES 300 check engine light on (smoke from under h

1995 Lexus ES 300 6 cyl Front Wheel Drive Automatic

I had my check engine light come on, been a few months now, mechanic said I needed (2) O2 sensors. I replaced all 3 sensors with new ones and still noticing smoke coming out of the engine, sometimes into the car you can see the fog a bit. Please help! I'm beginning to wonder if this mechanic just enjoys my company or something.