Somebody here will correct me if I'm wrong on this, but ...
I tested positive on first try, which surprised my doc, given how long I had been ill, so I didn't go through an abx challenge -- so take this for what it's worth: to my understanding, the point of the abx challenge is to get your immune system to step up and react, so that the tests will show positive indicators of infection, if you are infected.
The test results are the object of the exercise, not so much how you feel, tho you may Herx.
My symptoms have gotten significantly worse since starting doxy and I was retested for Lyme a week and 1/2 ago by my super-doubtful Hopkins intern. He said the lyme test came back negative, which I've heard before, so until I actually see the test results I'm taking what he says with 'a dose of doxy'. Anyway, I still have yet to be diagnosed by an LLMD, so In all honesty I'm shooting in the dark against whatever is wrong with me. Just wanted to comment as someone who was also hoping for a herx induced positive result and didn't get it:(
I never did an abx challenge. I started with Doxy and herxed right away. With any abx, I tiitrate up but even though my tests show I am still positive for Lyme, I hardly herx anymore.
Depending on what test you were given, it could come back false negative, meaning you have the infection but the test didn't pick it up. The basic Lyme tests are not accurate enough to be the last word, but instead are supposed to be data for a knowledgeable doc to view in conjunction with your history and symptoms. Most docs view tests of all kinds as completely accurate, and that's just not so with some of them.
I hope you will see an LLMD to be sure of the diagnosis. The tests are simply one piece of data, not + or - like a pregnancy test. Take copies of the test results, and always keep a copy for your own files.
I ended up not needing the antibiotic challenge as I was Igenex positive on my western blot. You could always call IGeneX and ask what they recommend for an antibiotic challenge. They're willing to talk to folks with questions.
I started with Azithromycin, and then a week later on Rifampin for Bartonella. At six weeks, I stopped the azithromycin and started Bicillin shots. I needed either Bicilin shots or Rocephin thanks to my late stage neuro symptoms.
I was usually also on an oral antibiotic for Lyme along with the shots. The oral med was switched out often. I have taken Biaxin+Plaquenil, Clindamycin, Doxycycline, and now Augmentin XR since I'm off the shots. There are quite a few others that are used in Lyme treatment. If you're curious, you can check out the treatment guidelines on the ILADS site.
I did not feel anything in paricular on the azithromycin, nor on the Rifampin. I was the slightest bit better a few weeks later when I had my first Bicillin shot. Within a couple hours I had horrific rib pain and also stomach and gallbladder/liver pain. I shuffled around as little as possible, hunched over holding my midsection. These were my areas of greatest torment and so they're the areas that hurt the most after a shot. I also had brain fog and fatigue. Each shot after had a little bit less pain in the die off.
I kept thinking I wasn't improving, but then when I looked back a month or two I could acknowledge that I was indeed better. It was slow going, though. Everyone is a bit different. Some don't really herx, they just start to feel better. Others are worse for months before the improvement starts. Also, in different people, different meds have different effects. I didn't herx on Biaxin, but had my biggest oral med herx on Clindamycin (narcolepsy-like fatigue, brain fog, and malaise), which I started 9 months after the zith. I was caught off guard as I didn't expect a big herx that far into treatment. I felt little to nothing on Doxy.
A side note: I believe I have the Australian version of a neuroborreliosis causing European species called Borrelia Garinii, a different species than the North American Borrelia Burgdorferi, but still within the group that causes human borreliosis. All the treatment experience in the US is on b.burgdorferi. There isn't a whole lot of studies done overseas on different species to know what works best for them. I just know that the penicillin family has worked really well for me. This is why it's important to have a decent LLMD. There is no cookbook treatment for late stage Lyme. It must be entirely customized to what the patient needs and responds well to. Feeling nothing on the first abx doesn't exclude Lyme, as you may need a different abx.
I *never* had a Herx reaction to meds. I had Lyme and babesia, and I just got slowly better throught treatment.
The size or existence of a Herx is not, to my understanding and in my experience, a reliable indicator of how effective treatment is.