Hi, Welcome to HCM and Thanks for asking your query here Choice of antibiotic depends upon many factors like severity of disease , susceptibility of bacteria from that particular Antibiotic and definately your Doctor would have thought every aspect of it before prescribing it Your doctor might have done vaginal swab culture and he might have found the bacteria causing illness is most sensitive to Flucloxacillin and so he might have prescribed it And as you already had taken Metronidazole before so bacteria might be resistant now to it this time your second query Regarding sex during the course of treatment - It depends on the cause of your vaginal infection. Medically speaking, it s OK to have sex when you have a vaginal infection (vaginitis) if the cause isn t a sexually transmitted infection (STD) and in your Case it is Bacterial so if you feel it pain free and comfortable there should not be a problem further I would advise you to take treatment regularly and consult with your doctor if you have any doubt about treatment plan and medicines I hope it helps Thanks and Get well soon