Katy I am so glad you posted this - not that you are going through it of course :( but I've a very similar problem with my own DD, & like you I have health problems so its a big worry,
not least because my DD was diagnosed with JHMS' in November, which her specialist said has close links with Fibromyalgia & since before Xmas she seems to have had one bug after another, so much so I've started to worry I've let her go back to school too soon & it my fault.
We were all floored with a flu virus over Xmas, DD started the week before & my health is at rock bottom, but I've put that down to my wearing myself out nursing her, our GP just says we have been unlucky & just keeping new viruses, but reading the replies on here, makes me realise there's a lot of it around, so our GP/ your GP is probably right & its not DDs illness getting worse, or that she has FM too
Have you tried Spirulina for your DD Katy - it does help, though for DD not as much this time round as with other illnesses, she does pick up when she's taking it
Hope she's better soon, I'm sure it's the last thing you need too xx