I also had Group B Strep with my third and I went on a rampage to find any information as I could as I too didn't get very much information on it. My midwife stuck an alert sticker on my notes and I was made to feel like I was HIV positive it was horrid!
You need to tell your midwife on your first appointment, the problem with GBS is that although one day you may be positive the next you will test negative and considering how serious it can be for the unborn child they do not routinely test for it in the UK only in the USA. Unfortunately opting for a C-section does not erase the risk of GBS on your unborn child hence why they should use IV anti-biotic's during labour, they aim to get at least one 4 hour dose in before the baby is born.
You need to make every person who you see aware just so they can treat you accordingly, although it doesn't cause for great concern unless your waters are to break prematurely i.e 48 hours before your labour starts as that can pose a threat to the baby.
The thing is even with antibiotics, it doesn't completely prevent it just decreases the chance of you passing it on and it only prevents early onset GBS which happens in the first 24 hours of birth usually and can be sorted quite effectively, there is a risk of late onset which usually comes about within 2 weeks and anything up to 3 months but late onset GBS at 3 months is quite rare.
I had IV antibiotics with my third and my waters broke at 9cm dilated which in my eyes was the best possible outcome as she was born about 5 minutes after my waters went. I was scared at the time but with this pregnancy I'm currently 17 weeks I feel fine about it, just do your homework avoid the horror stories unfortunately they are out there but my labour was fine, in fact it was the best I had out of all three!
GBS is common affecting 30% of women in the UK, you don't carry any symptoms and strep throat is completely different not to be confused with strep A e.t.c e.t.c. Baby can get GBS from your amniotic fluid rare but can happen, usually baby will contract it through the birth canal.
Hope this has helped. You will be fine it's a 1 in 200 chance your baby will get GBS and they will keep you in for 24 hours for monitoring to ensure all is well but my experience is only positive.
All the best.