Is there a way to tell if my doctor really knows anything about fms?

Ask him or her. Your best bet is always to level with your physician. Ask dirctly and if you are not satisfied you can also ask would you recommend I see somebody else. We don't always have all the answers. There can be many options.
Second opinion. Fibromyalgia is a relatively common disorder so it is unlikely that your doctor does not know about it. You can always get a second opinion if you are not getting better. If you are getting better, then no need. Don't worry what the doctor really knows; the medical community knows very little about fms as it is.
Talk With Them. There are many doctors who have a lot of experience in treating fibromyalgia. Some primary care have a special interest as well as some specialist, including rheumatologist, pain management, and physiatrist.