Hello, On Cd 13 There Were 2 Folicle On My

Hello,
On cd 13 there were 2 folicle on my right ovary. One was 23mm and the other around 21mm. Now I am on cd15 , and opk is building up I think tomorrow it will be +, today is the same color as test line. I I not on any medication never have been. So my question is why there are 2 follicule and will the egg be over-mature since follicule are too big. What are the normal size. No POCS diagnosed. Regular 26-28 cycles. Only thing I have is dismenoreha.thanks