Severe yeast infection that isn't relieved by canesten or vagisil and hasn't gone away after taking fluconazole?

Maybe not yeast?: It is very rare that yeast would not respond to one or more of these treatments, so maybe not yeast. With "severe" symptoms and especially if there are open sores, herpes is a possibility. If you've been treating this yourself, it's time to see a doctor for professional diagnosis; or if already in care, perhaps get a second opinion. An NHS GUM clinic would be an excellent source for expert care.