Sorry to hear you aren't finding answers to your ever increasing fatigue. I can only speak from the Lyme perspective as our son has extreme chronic fatigue as one of his worst symptoms with Lyme and other tick infections (mycoplasma, babesia and bartonella).
If you do take antibiotics targeted toward Lyme you will probably figure out if it is the cause pretty quickly, because many who are become either suddenly well (sometimes for just a few days before they get worse unless the bite is very recent and yours isn't) or they feel even worse, depending on how long they've had it. This is because of the sudden die-off which causes the Herxheimer effect plus new symptoms can arise. Our son became incredibly ill while on the first month of antibiotics. It really helped confirm some of what we were going to be dealing with. He, however, had a very positive Lyme test but had Lyme etc for several years before testing and thus had many co-infections that had progressed. Not everyone - yourself included gets a + test - but that doesn't mean you don't have it.
Hope this helps a bit and good luck with whatever you decide to do.
Parent of 14yo DS with +Lyme test in Nov 2015, co-infections: mycoplasma (strongly +), babesia, mainly with antibiotics/anti-malerials. Supplementing with Vit D, Vit C, Vit B-12, multvitamin, milk thistle, dandelion, nettles, Burbur/Pinella, L acetyl carnitine. Magnesium oil, charcoal led to shorter herxes.
Website I started: ParentsofLymeKids.com