Hi M.,
I am so sorry to hear about all that your little one is going through. I know it's frustrating, to say the least. I have a few thoughts for you.
First, I have to echo everyone else's suggestions about documentation. This is critical in a situation like this when it's not clear what the problem is. When you document everything like fevers, etc, you need to include tests run (and the dates they were run, and where) and results, doctors seen and what they said and did, dates they were seen (and where), plus duration of the illness. This helps doctors keep track of stuff if you happen to see more than one provider. If possible, see if you can get copies of any tests and labwork to keep together in a file, and take those with you to doctors appointments.
Go back to your child's doctor and start pushing a little harder. Clearly something is going on, and it sounds like something bigger is going on. If you aren't satisfied with the response, then get a second opinion, and then, if needed, a third, Don't be afraid to get pushy. This is your child...if you feel something is wrong (and I agree with you, it sure sounds like there is something wrong) then something needs to happen pronto.
I see that you live in Moscow. I know that's a ways from Spokane, Washington, but there are two children's hospitals there...Sacred Heart Children's Hospital and Shriners Hospital for Children. Now might be the time for you to advocate for a referral for a work up at one of those hospitals. I don't know what your insurance situation is, but great thing about the Shriners hospital system is that they provide care regardless of ability to pay.
Also, I'd encourage you to stay away from the internet at this point, and to respectfully request that your friends and family not give you their diagnosis and opnions. All this does is scare you needlessly. Frankly, you don't need anyone upsetting you anymore than you already are. The symptoms your child is displaying could be anything, and I mean ANYTHING, and right now you need reassurance and support, not fear and more concern heaped upon you. Don't be afraid to stand up for yourself and let others know what you need or don't need right now. The same goes for the internet...all it's going to to is scare you and you don't need that right now, do you sweetie? :)
Hang in there. I do hope and pray it works out for the best. Please let us know what happens!