First, PM docs have heard it all & seen it all. They've heard every story in the book and I'm sure when he spends that hour with you, he will try to determine what exactly you're there for. Playing "dumb" is generally not a good idea. Again, the doctor has probably heard that whole routine a million times. Just be honest and tell him how the pain affects your life, what level the pain is at and what you expect to get out of this treatment. You want relief, plain and simple and that is what the PM doc is for.
He will ask you what treatment you've tried in the past, all the doctors you've seen for this condition and medications you've tried. Depending on your situation, he might not prescribe anything right off the bat. He might order you to try some alternative treatments before resorting to opiate therapy. Again, this all depends on your ailments.
Don't tell the doc you buy pills off the internet! That will probably end the session right there. BUT, when you first sign up for treatment with a PM doc, you will have to sign a very strict agreement stating that you will not obtain narcotics from any other doctor, can only use one pharmacy to fill all your prescriptions, never take more than prescribed amount unless you first talk to the doctor, and in some cases, this agreement will state that you might have to come in with your medication to show them that you have not been taking more than precribed, e.g. count your pills. You really have to be disciplined, but more important, honest with the doctor and phone him immediately if the meds aren't working. Never take more than prescribed because they can and will terminate treatment.
PM treatment is a serious thing, but to get the results you want, you have to be honest and forthright, and also not use OPs anymore. From what I hear, if you get the right doctor, you will get exactly what you need to manage your pain. Good luck!