i'm just throwing this out there, but it may be a stretch...
when i was last on iv abx i got better for a week and then all of a sudden took a nosedive and FEV1 went down to before abx and i felt awful. my sats dropped and HR was elevated even with just standing in my kitchen. it was terrible and scary. i also felt sob all the time and tired and crummy.
i ended up in the ER with severe pneumonia. they have no idea how i got it being on abx and not leaving the house for that first entire week. they said it appeared to be bacterial, which makes even less sense.
... but, the only thing they could figure out was that my body was somehow building up an allergic reaction to one of the three meds i was on. or some sort of adverse reaction that, once started, just plateued into a really terrible infection that the abx couldn't touch. it was strange. docs were a bit perplexed, but pretty sure that it was likely a reaction that just "took over" my system allowing all sorts of bad bacteria to start growing.
i think this is a rare thing, and i'm not entirely convinced that's what it was. we switched meds to treat it and i still never got feeling that well. i was able to improve my FEV1 but not like i used to.
i did get back my "normal" 96% sats about two weeks after all this took place, but still never felt amazing. i still don't feel amazing, but again am not sure that's due to the "complications" of that abx treatment OR whether its just worsening disease. especially since the time before that i didn't feel a whole lot better either. so, i'm just chalking that feeling up to worsening disease.
moral of the story is that maybe, just maybe you are having some sort of reaction to the meds that is in fact making your symptoms worse or making you sicker. again, i think its rare and am not even entirely convinced that is what happened to me, but if you were on the abx with little to no effects and then now, as weaning off them, you're feeling awful, it could be your body's reaction.
maybe i'm way off here, but thought i'd share what happened to me so you could compare with your symptoms and maybe bring it up to the doc. feel free to PM me if you want to chat further about it.
i hope you start feeling better soon. you're in my thoughts...