hi doma,
"All medicine is a Placebo"
No. This is incorrect. They test new medicines against the placebo effect. Only those medicines which exceed the effect of placebos in the double-blind trial end up at the chemist/pharmacy.
That isn't to say drugs are 100% effective. Their effectiveness depends upon the environment they enter. Apparently, genetic differences and perhaps the composition of the bacteria inhabiting your body make a difference to efficacy.
"......that's why the antibiotics are no longer working!!"
I'll go with the standard explanation. Bacteria evolve. The ones that survive antibiotics are the ones that thrive.