Welcome to MedHelp. Sorry to hear you have had such a hard time -- it's not unusual, unfortunately, judging by stories similar to yours that many have posted here, and given my own rather similar history.
If you haven't found out yet, there is a split in the medical community about Lyme and other diseases carried by the same ticks. The Infectious Diseases Society of America (IDSA) holds firmly to the idea that Lyme is rare and easily cured with a couple of weeks or so of antibiotics. The other position is held by the International Lyme and Associated Diseases Society (ILADS -- see website at ILADS [dot] org), which holds a more flexible position, that Lyme is a complex disease that presents with a variety of symptoms and co-infections, and that due to certain characteristics of the Lyme bacteria, a short course of antibiotics may well not be curative unless given very very soon after infection; ILADS views a Lyme diagnosis as one based on symptoms, aided by the not very accurate tests you have already had.
In short, there is a war going on in the medical community, and the patients are caught in the cross fire, as you have been.
Some decades ago, the first diagnoses of Lyme were made by neurologists and rheumatologists, who claimed the disease as belonging to their own specialities, so that even now, if you don't have (for example) swollen knees, some MDs (esp rheumatologists) won't diagnose Lyme. (I'm always put in mind of the old story of the blind men and the elephant: each one describes the elephant by the part of the beast he happens to be touching.) The fact is that Lyme is easy to get, the diagnosis is not terribly straightforward, and treatment can be complex.
You are asking the right questions, and I hope that you do not have Lyme, but if you got it, you got it. The next step I would recommend (and I am NOT medically trained, so don't rely on me or this website for medical advice) is to find what is loosely called a Lyme Literate MD (aka LLMD), one who is more in the ILADS camp, taking a broader view of diagnosis and treatment of Lyme and its co-infections.
The tests that you have had done are helpful, but it's the interpretation that matters. If you go to a website called www [dot] truthaboutlymedisease [dot] com, there is a page listing all the 'bands' that may show up on a Lyme test such as you have had already. It is good news that your MD ordered Igenex testing, because it's the most reliable. The trick is interpreting what the tests mean, and for that you need an LLMD (imho).
Your Igenex test results may indicate an infection, esp. band 39, which is specific for Borrelia burgdorferi, the bacterium that causes Lyme. Some of your other positive/ideterminate bands may indicate Lyme or something else. The fact that your bands are somewhat weak could mean simply that your immune system has slowed down fighting in an obvious fashion and is not producing antibodies as it would earlier in an infection. Therefore the tests are helpful, but not definitive. (Sometimes LLMDs will give a short course of antibiotics, called an 'antibiotic challenge', that causes your immune system to get more active against the bacteria, and so your tests may then show a stronger positive reading, thus aiding diagnosis.)
The upper midwest including Michigan is a well-known Lyme hot spot, so it's not unusual that you could have been infected. Lyme is actually throughout the US and much of Canada, as well as Europe, and there are many strains that cannot be tested for yet. That you have a slight positive may well mean something, and I would encourage you to find an LLMD and get a work up. Take all your existing test results with you.
B. henselae is a common coinfection of Lyme, often called simply Bartonella. It's a separate disease with its own symptoms and treatment. Perhaps you were also tested for other common coinfections and came up negative. I recommend that you always get copies of ALL test results for your own file.
I'm not terribly surprised that the neurologist didn't take your situation very seriously. Neuros often have a very narrow view of Lyme and are tightly bound into the IDSA point of view. (If you are up to it, I recommend looking at the ILADS [dot] org website treatment guidelines. It's complex but understandable.)
So I don't know if you have Lyme and/or bartonella, but if I were in your shoes, I'd get me to an LLMD for testing and evaluation. The sooner the better, because the diseases are easier to cure the sooner you are treated. I've had many of the symptoms you report, and the ones I haven't had, others here have reported.
So yes, you may have Lyme+. The good news is that you are still persisting in finding out what is wrong and getting it fixed. Let us know if you need help finding an LLMD in your area. We don't post LLMD names in public here, because there is sometimes harassment of LLMDs by local medical boards who oppose the long term antibiotic therapy sometimes used by LLMDs.
Stop by again and let us know how you do going forward and what you find out. Best wishes --