I need help ladies.

Okay I’ve been taking ovulation tests every day usually twice a day for a month. I had cd 1 February 10 I’m on cd 13 In this whole time taking ovulation tests I have yet to get a positive. I know I’m fertile bc we have 6 children. (Our baby is one.) I am using the easy at home brand. Any insights? I usually test around 11 am and 3 pm. Then for a while I’d test 9 and 11 am. Then 3 and 7 pm. Any thought about why I haven’t gotten a pos opk?