What Causes Missed Periods And White Vaginal Discharge?

I have missed my periods this month.I am 47 year old lady. I missed mine thrice earlier some one year back. My vaginal discharge looks like thread and white in colour. I have such discharges for the last four days. But it comes only once. Before this during my menses, there has been foul smelling (some fish like smell) around me. This has been for some 10 years I can say . I consulted many doctors but there is no cure. All the doctors said I am absolutely alright. What is my problem exactly?