follical size confusion

Janna • Mom to angel twins born sleeping at 18w and a chemical baby. RIP Maven and Macie and Littlefoot.
So my doctor and I are trying to pinpoint ovulation so I can start progesterone. 
CD14: no dominate follicles. Right ovary 4.4x3.2x2.2
CD21: follicle at 13mm. Right ovary 2.9x3.1x2.2. Doctor sends me a note saying I'm not ovulating. 
CD 23: positive opk in evening but no other signs of ovulation.
Questions: is it possible that the 13mm follical grew big enough to ovulate on CD24? And is it normal for an ovary to change in size? 
Thanks in advance!