I had GBS in my second pregnancy and I did something similar to this in my third including garlic and occasionally yoghurt vaginally at night. I have started again at 31 weeks as I don't want to be positive this time at 36 either. So far I'm taking:
(Ps this is my personal choice and this is in no way medical advice that you can get from your doctor. It's entirely up to you what you decide to do.)
2 raw garlic cloves cut up into little pieces once or twice a day
4x probiotics
yoghurt or kefir orally once a day, sometimes I have kombucha, if my life wasn't mad right now I'd make it myself, so much cheaper
apple cider vinegar 1 tablespoon with 1 tablespoon of honey in a glass of water once a day and a bath with 1/4 cup every other day
vitamin c 500mg 3/4x per day
I haven't done anything vaginally yet but I'm 32 weeks now and I may start doing two days of garlic one day of yoghurt at night and probiotics in the morning vaginally but I may stop the probiotics at 35 weeks as I've heard of false positives.