First let me commend you for taking charge of your body and researching what you are feeling. And for not being afraid to disagree with your mom and doctor. I did the same thing, and if I hadn't I would still be with a doctor who believed it was "all in my head" and my parents would still be calling me a wimp!
That being said, you need to find a doctor you can trust, and maybe a guardian to bring with you to your appointments that you can trust as well - that is until you are 16.
You are not a wimp, and some would even consider those of us with FM stronger in the sense that we have to tolerate and push through pain on a daily basis. We have to learn how to do things differently on our own so that we can continue to do the things we love.
But it's not the end of the world!
My physiatrist gave me an awesome elimination diet to help:
Foods to avoid: potatoes, chick peas, lime, lemon, raw onion, raw garlic, alcohol, tomatoes, grapefruit, grapes, strawberries, raspberries, peaches, kiwi fruit, cranberries, eggs, white flour, white sugar, vinegar, no yeast products, watch milk products, no bread except for rye and pita.
These are foods that are commonly known to increase flare-ups and worsen symptoms in FM sufferers. After two weeks, start reintroducing the items listed one by one and see if you notice and increase in your pain, if you do, you know to avoid that item.
That being said, it won't cure FM, if that is what you have. In the absence of any other conclusive finding via blood, urine, scan tests, you may find that you are diagnosed with FM. There may not be a cure but there are ways to manage the pain and help you cope.
You are doing the right thing in questioning what you are being told if you feel that you aren't being heard properly. You are lucky that you are so in tune with you body to know that there is something going on that you can't explain, it's the first step to figuring it out. The next is to find a doctor who recognized FM as a real condition, because it is. If someone tells you it's "in your head", they are being ignorant and unhelpful.
Surround yourself with people who want to help you, and know that you are not alone. There are so many of us who have been in your shoes at one point, and we are all here for you if you need us.
You may also want to see if there is an FM support group in your area that you can go to. You may be able to get a referral to a good doctor who can help you.
Keep pushing through, you can do it! And remember, stress can make this condition much worse, as hard as it is, try to avoid it as much as possible. If you feel that you are getting stressed, remove yourself from the situation, if possible, and revisit it later.
Good luck, PianoPlayer.