Hi Meid and welcome to KA.

I truly hope you do not have AS, but if you do, at least it's an answer, yes?
I would suggest you make a list of your questions and put a star beside the three that are most important to you personally. Then hand the rheumy the entire list to look over, in case there's something on it that's medically important and requires attention.
There is a pain map on this site (I think it's linked off the first page????). Colour in the areas that hurt - perhaps you could use red for severe pain, orange for moderate pain and yellow for slight pain (just suggestions).
Also, write down how your pain is affecting you. Is it making it difficult to wash your hair, get dressed in the morning, put dishes away, walk any distance, sit for any length of time. Also note whether you have morning stiffness, and if so, how long it lasts.
If he's going to order blood work, ask what type and make sure he includes ESR (or SED), CRP and HLA-B27. The first two measure inflammation in the body (although not everyone with AS shows elevated numbers on the ESR test, the CRP is usually accurate), the third is a genetic tissue type that about 93% of people with AS have.
Also, I would take in a list of all the meds you've tried and whether they worked at all. Your pharmacist may be able to provide one from your files. Just put a star beside anything you are currently taking.
And do not be stoic about it. He needs to know just how badly this is affecting you. It took my first rheumy a while to realize how stoic I truly am, but the second one figured it out in a nano-second. The first rheumy is truly good and the only reason I have a second one is that he is an AS specialist who works with and researches biologic meds, as well as genetic links in AS. My first rheumy referred me to the second one when I got ulcers from NSAIDS and needed something more direct.
That should get you started. As I said, I hope you don't have AS, but if you do, you've just joined the best bunch of people on the planet here at KA! Especially if he tells you it's all in your head!

Sorry, not really making light, but too many of us have heard that.
Hugs,