I am 37+ weeks and have just received the news that I tested positive for GBS. I have heard of some natural treatments, but I wondered what advise you might have.
I'm afraid I can't help you. I have just reviewed the last 5 years of GBS research on PubMed and didn't find a single study of natural treatments. All I could find was a review of trials of a chlorhexidine vaginal wash in labor, which had some effect in reducing skin colonization in the newborn but even in the aggregate, didn't have enough people enrolled in the component trials to determine if it would reduce early-onset neonatal infection. In any case, that would hardly count as "natural" treatment.
I can tell you that use of antibiotics in labor works. If you want the nitty gritty, here is where you can read the CDC's current guidelines: http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5910a1.htm and the reasons behind them. I think your best bet is to agree to antibiotic treatment and use natural remedies to try to counteract its downside, which is killing off the friendly bacteria as well, by using probiotics. Midwives and lactation consultants can often advise you on this.