Just chiming in with TrudieC, here. :) Don't be afraid of the rheumie! He or she wants to help you. Go in there armed with every scrap of information you have, like Trudie said. There are many kinds of auto-immune diseases, not just arthritis, so make sure your family history lists all the diseases that you're aware of, as many generations back as you can find out about. I've read that diabetes often runs in families alongside the RA, and so do certain eye diseases, so even if a disease (like grandma's glaucoma) seems unrelated, document it.
Visit the Arthritis Foundation web site for lots of information about what kinds of tests you're going to get. Write down a list of all your questions and concerns and take it with you, and insist on getting them all answered to your understanding.
And, like Trudie said, hang in there because it might take time to get a diagnosis and then to find the combination of meds that work for you. There's no "one size fits all" when it comes to diagnosing and treating autoimmune disorders.
Good luck!
Good that you are getting into a rheumatologist. It is important that they treat the disease and not just the symptoms.
On your first visit take a listing of all drugs, vitamins, supplements, etc. that you take and the dose. Bring a family history of any auto-immune or arthritis issues. Be ready to fully explain all your symptoms (remember skin issues, headaches, memory issues, etc. can be related to arthritis so leave nothing out).
They will take oodles of blood tests and you will likely need to supply a urine test.
It might take some time to get a proper diagnosis but work with your rheumatologist and keep getting tested if you don't get answers right off. Good luck and please let us know how it goes.