Multiple days getting +opk...?

Kristin • Married 2014👰🏼 miscarriage October 2014🌈baby boy December 2015💙 #2 due July 2020💕💙
When getting multiple days of positive ovulation tests I heard go off my first positive, that true? 
Why do you get multiple days positive? 12/25-27(today) all positive??? Normal?