It's not 'it MUST have been the last thing I took'. I see it as: 'I tried a whole lot of other stuff. That didn't work. I tried this, something changed.' Which makes me think there's a greater than zero percent chance the change came from the last thing I took. That's not a strange thing to think is it? Causality wise? As for the placebo part, wouldn't it make sense for that to have worked during the other treatments?
Personally, yes, it is strange. But for the majority of people? Probably not. But what other things happened that were different? That's the thing. Usually in these situations people don't properly analyze what was different during each treatment. There's less than a zero percent chance that it went away anyway. Why even attribute it to homeopathic "remedy"? Homeopathy is based on "like cures like". This isn't scientifically sound in any way. In fact, I've never heard of the mechanism by which this would work by homeopathic "doctors". As posted above, the dilution thing is hogwash.
Not necessarily. People respond differently to different things. The mind has a lot of power. In fact, being in a good place mentally helps immune response. If one believe this think might work because the others didn't, it might simply because of the mind.