How do I find out if I have arthritis?

Doctor visit. See either your primary or be referred to a rheumatologist to have a rheumatoid panel run, a blood test and probably x-rays to the affected body parts.
See your PCP. There are many different types of arthritis. The best way to start to figure out if you have one and which kind you have is by seeing your primary care doctor for a careful history and physical exam.