Your GBS status can change from week to week, let alone from pregnancy to pregnancy. Women who test positive have a 0.5% chance of having an infant who contracts GBS disease, which can be fatal. Standard treatment is to administer IV penicillin to all mothers who are GBS+ while they're in labor, and this has been shown to reduce infant transmission, but not infant deaths. Mothering has a great article here:
http://www.mothering.com/articles/pr...n/group-b.html
and I have a word document that I'd be glad to email you that has more numbers in it. PM me if you want it.
Treating with antibiotics in labor carries its own set of risks, so I would do your research and talk seriously with your doctor about those risks before making a decision about whether or not you choose to go that route.
You can also try to un-colonise yourself through a regimen of probiotics and the like, there are several threads here that can help you, and then request a re-test. Good luck.