The thing is that these tests just are not sensitive enough, so many of us will not test for everything we suspect (lots of LLMD's will do clinical diagnoses!), and to save the money for treatments.
The tests rely on either immune response or detecting the bacteria directly. The main reason they are not sensitive enough has to do with us having Lyme, which lowers our immune response, so not enough antibodies are being produced to get a fully positive test for many of these infections, not just Lyme.
As for the direct measuring of the bacteria (PCR), it only takes a very small amount of bacteria to cause a serious infection, so if the blood drawn doesn't happen to have the bacteria in it, you will have a negative test, even though you still have the infection.
As for your diet, this is one resource that may be of help:
www.glutenfreeandmore.com/ I don't follow a gluten free diet specifically because a soy allergy keeps me in line pretty much - but there are plenty of others that will be along to help point you in the right direction. If not, please do start another thread - plus, don't forget to use the search function here to find more ideas of gluten free diets!