OpK issues

Megan

Last month was my first time using opks, the second line got darker everyday until cd 14, this month I'm on cd 15, still no second line, but watery/ewcm for 3 days.

Are the tests not working well, how many days should I keep testing? I feel like all the other ovulation signs are there except the opk

We are trying to BD every other day this month, so cd 13,15, and 17.

Normally a 28-30 day cycle