Opk cd5&6 letrozole

Ca

It’s my first cycle taking letrozole 2.5mg and I felt a few twinges yesterday. I took an opk last night fully expecting it to be negative but it was almost positive! I took another this morning just in case and this is what I got. Does anyone know if it’s normal to ovulate this early on letrozole?! I usually ovulate CD15-17!