OPK question

Amber • 7/1/09 miscarriage (8w2d), 5/31/10 my son was born, 5/26/15 chemical, 6/24/15 chemical.
So on 6/8 and 6/9 (first shown) I got positive OPKs, 6/10 negative (middle one) and today positive again. App says I Oed on the 9th. 
Why would they be positive, then negative, then positive again? All were using FMU around the same times in the morning like I always do.