can glow be out with ovulation dates

Jennifer • Angel baby in my heart 27/01/017 married 01/03 rainbow baby in way EDD 15/12/2018
Reason i ask is because i have been using opk since hlow told me when i going to ovulate and to them yesterday was my ovulation date, but when i tested the line wasnt stong.
However this morning  the line i took this morning is a lot stonger the test line and ive had cramping on my left side....