Need Help - 1st Month Using Opk

Gianni
I am not sure what day is considered positive! They all look positive to me but I am thinking Day 15 is the true ovulation day but it looks very similar to Day 14. 
The following 4 pics were taken on Days 13-16. The single pic was taken this morning on Day 17. I haven't noticed any change in my CM so I am not really sure if this I have ovulated. 
What are your thoughts?