Blue smoke

I have a 1994 Toyota Camry SE V6 that emits lots of blue smoke that smells like burned oil when the engine is cold. It has a slow acceleration and uses more oil than usual. It all started after the transmission was replaced not so long ago. I took it to a mechanic and this is what he did to it. He replaced the transmission, spark plugs and a tune-up. When I got my car back, I noticed the blue smoke when I turned the car on. The mechanic said that it was due to an oil change, so it would be normal to expect some smoke and burned oil smell. A couple of days later, I complained to him about the smoke and he said to change 3 spark plugs to those that could withstand higher temperatures. So, after looking up online of the possible cause of my problems, I changed the front valve cover gasket, but the smoke has remained the same. I also noticed that a small amount of the blue smoke comes from underneath the exhaust manifold.