My problem differs from most that have asked this similar question.

6 months ago I had to replace my old leaking cast iron p-trap and drain in my shower. I replaced it with a PVC P-trap and new drain. I used a rubber gasket with a couple pipe clamps to connect the new PVC trap to the existing cast iron pipe. It has been working great, and no more leaks... but now a sewer smell emits from my shower drain. It couldn't possibly be a blockage since the Trap is only 6 months old? Is there anything I should check or can do to get rid of this powerful unpleasant odor??

In advance thanks for all your input and help.

"couple pipe clamps to connect the new PVC trap to the existing cast iron pipe" well there's your problem, OVC doesn't seal againist cast just by using hose clkamps. You need to use something like a Fernco adapter to make a proper seal. Right now you are getting raw sewer gas off the connection after the trap. Fernco, Inc. (http://www.ferncoconnectors.ca/1056.asp)