Clindamycin is active against a
broad range of pathogens, like most antibiotics. Among those are bacteria like Staphylococcus aureus, which has been linked to certain chronic diseases. If you take clindamycin and start feeling better, how would you know what the cause was unless you get tested on beforehand with some reliable test, which doesn't seem to exist in this case.
It's basically the same problem as with Lyme disease in that there are lots of tests that show false positives or false negatives and lots of people who don't improve with any antibiotic while some do. Since most of us humans harbor tens of thousands of bacterial species, even having demonstrated you found "pathogen X" in the blood and then get better following a broad-spectrum antibiotic does not prove "pathogen X" was causative, as it could also have been "pathogen Y" causing all your symptoms, which the antibiotic also happened to be active against. Many antibiotics are also anti-inflammatory, which is one hypothesis why some people with chronic diseases notice improvement while on them, but then regress once they stop.
Anyway, forgive me for my rant and I'm happy you found something that made you much better and that you shared it with us. Those kind of recovery stories are so rare that they are always valuable. The antibiotic regimes tried for Lyme disease have not helped most of us here, but there may be some novelty to this approach as clindamycin is not an antibiotic that is typically prescribed, so it could be that it helps ME/CFS patients in let's say more than in 1% without us knowing.