And the verdict is...

The doctor called me today to see how I was doing and to tell me that he figured it out! I have Fifth Disease, or a parvovirus (completely unrelated, though it has the same name, as the virus that kills dogs). This virus hits most people as children, so almost everyone has already had it and is immune to it now. Except me. Apparently, I never got it as a child. When children have it, they get a rash, a low-grade fever and within 7-10 days, it's completely gone. For most of that time, the child acts pretty normal. When an adult gets it, it hits harder. There's joint pain and a couple of other things that some people get and others don't. I apparently got the joint pain. The doctor told me there wasn't anything he could do for me, since it's a virus and it may last for months. Which, you know, is encouraging. =) But, it's nothing serious, it will go away and in the meantime, I just keep popping Ibuprofen.

So, now we know! That's a relief, at least. I'm glad that I know what's causing it and that it's nothing serious. Thanks for your prayers and support! I love you all!