Hi Dr, I Am Using Siphene 100 From 23/04/2015 Continue

Hi Dr, I am using siphene 100 from 23/04/2015 continue for five days. I want to my ovulation day. Is ovulation occurs once in a month. My period date was 19/04/2015 to 23/04/2015. Last month period was 06/03/2015 to 09/03/2015. Age 31 Date of birth 19/05/1983. Thanks for ur time