It sounds plausible, the Antibiotics lower resistance and leave you vulnerable to opportunistic infection. Unless you can target the exact source of the infection it doesn't matter what the cause was, you need to restore your immune system, which leads back to what I posted above.
If you ate a known poisonous mushroom then you can target restoring liver function.
I think it is rare for people to have success by focusing on the initial cause, no matter how tempting it may be. You have to realize you are in new territory now with a whole cascade of immune system failures that need to be addressed. The good news is that you have a chance to become healthier than you were.