Confidential, yes . We provide utterly confidential advice and treatment, and even if we didn't provide treatment to some individual the fact of asking would remain confidential.
Girls can have advice and contraception before sex, or after.
The former works better. We may even broach the subject for no apparent reason. British Medical Association statement on it . Either Nurse will sort this out for you. How long do common diseases take from first contacting a sufferer, to either developing the disease or being safe to mix with people you don't want to pass it on to.