Confusing question

Chelsea • 31 years old, married for 5 years, and have a 2 year old little boy! 👶🏼💙
Ok so I ended my period on March 4-5. On March 7, I decided to start testing for my LH levels just because I not very aware of when I'm ovulating or when my fertile window is. I've taken an OPK on March 7, 8, and 9 and I'm very confused by the strength of the test color from Saturday to today (Monday.) It makes me think I was fertile on the day I was done with my period. Feedback would be extremely helpful right now! Thank you! 
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