We were in a similar situation and I can vouch that taking the abx and waiting for a response worked in DS' case.
DS started 2 weeks of Rifampin a month ago and it was at the end of that month (last weekend) that we noticed the tell-tale stretch marks on his back. He also had white small dots at the top of his spine which now after starting cycle 2 and 2 days of pulsed Rifampin have gotten bigger, turned pale pink and are raised like welts.
He wasn't tested for bart but LLNP treats for it - he had some behavioral symptoms but no physical ones for that co-infection. Turns out he has it along with at least 2 others.
Good luck - I say treat in some fashion is probably a great idea because it is the 2nd most common co-infection according to what I read on LymeDisease.org.
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