Hi twinmummy, please try not to worry!
I am fairly sure that there are other antibiotics to treat GBS.
In my NHS pregnancy handbook, it says that people pay to get tested privately as it's not available on the NHS, so it's pretty much expected that people will do this. I think your midwife will just put a note in your notes that you are GBS+ so everyone is aware. Have a chat with her about the antibiotics and what to expect in labour.
Another thing to consider is that - thousands of women are GBS positive (about 1/3 of the population). Most babies are born with no complications, even to women who are carrying GBS without knowing it. It is very rare that a baby will get it.
On the other hand, it is best to be prepared and get all the help and treatment you can get as it's such an awful thing if a baby does get it. It is best to prevent it as much as possible and it's good that you know that you are GBS+ before the birth.
My daughter had late onset septicemia from GBS at about 2.5 weeks. It was totally unexpected as I had no symptoms of anything, I was not aware that I was carrying it (and still not sure if she got it from me) and I'd had a planned C-section which is supposed to more or less eliminate the risk. She became very ill and we almost lost her, but thankfully she pulled through and has been fine ever since. Now 3 and a handful!
I'm pregnant again and quite nervous as my risk is increased for another baby, but in a way I feel more prepared that the medical staff will know and treat me accordingly.
Have you been on the GBSS website, hopefully that will give you more information.
Ahhh. Just had a look, see about the third paragraph down, they will use clindamycin if allergic to penicillin.
Good Luck - when are you due?