Vaginal candidisis or genital candidiasis is the common cause of vaginal infection & itching. Closteridium difficile causes bacterial vaginosis and responds to Flagyl (Metronidazole). It is a drug used against anerobic infection. Vaginal candidiasis is a fungal infection and will not respond to Metronidazole. Doxycycline is a broad spectrum antibiotic, more useful in infections due to gram positive, gram negative bacterial infections & also against ricketsial & chlamydial infection but not against fungal infections. To treat mixed infection (due to fungal, anaerobic & bacterial infection) combination kit consisting one antifungal drug, one antibiotic & one drug against anaerobic infection is available. But since your infection is minimal, Clotrimazole vaginal gel application 2 - 3 times a day in the affected area for 2 weeks is adequate. Side effects like local irritation & stinging sensation occurs in few & not in all.