I don't think there is anyting wrong with using plastic, as long as there are no nicks or scratches on the inside where the nasties can hide.
A gushing bottle can be a sign of infection, but not necessarily. Perhaps you bottled too soon. Is there a telltale ring on the neck of the bottle? That's a good sign of infection.
"That oxygen powder"- I assume you mean OxyClean? Oxyclean is an excellent cleaning agent, but it is NOT a sanitizer. Use your OxyClean to clean, then your sanitizer to sanitize. If your sanitizer is bleach, you must rinse rinse rinse. That means that the last thing to touch your bottles (other than your beer) is your rinse water. Do you have well water? Have it tested-It's probably not the source of your infection, but at least you'll have eliminated one possiblilty.
As AHammer said, don't give up, you'll figure it out.