confirmed u/s ovulation but 1dpo dip?

Whitney
Hi! I took clomid days 3-7 of this cycle and had an ultrasound today at cycle day 15.
I've been taking opks and got my first positive yesterday (I wouldn't say it was definitely positive but close enough that it may have been). I figured it would be a for sure positive today but it was less strong and an obvious negative today.
My bbt dipped .4 degrees today which is weird... but at my appointment they said I had two follicles and fluid indicating I had probably ovulated yesterday? Anyone have any insight