once the first big water damage (toilet tank overflow) happened, mold began to establish itself. It may not have been visible or significant.
The second big water damage is NOW, and that enables the mold to grow like wildfire.
Both are not your fault. You did not cause it.
You now live in a poisoned house. Mold -- when there is too much of it -- will produce smells, odors, mycotoxins, that will make your immune system go into high gear and work extra hard to defend the body against these complex chemicals. Too much of it will make your immune system work extra hard, and that is the source of health problems. A weakened immune system, allergies, sores that take a long time to heal, and more.
The shower plumbing now leaks. That much you already know. That is not your fault.