If I were you I would flush any prescription for tetracycline I was given down the toilet. Broad-spectrum Antibiotics like that are the worst thing you could possibly take for your gut.
As for ways to knock back the pathogens, I highly recommend 1) Miracle-Mineral-Supplement (worked miracles for me) and 2) oregano oil and/or grapefruit seed extract. I honestly can't imagine Miracle-Mineral-Supplement in particular not being a major help.
I would also start taking a S. Boulardii supplement, which is a probiotic yeast that is famous for helping restore normal flora in people with bacterial infections like C. Diff. It is also excellent for diarrhea.