I am on CD 14 following a chemical and i am waiting to see a positive too, its my first time using OPKs and i am getting impatient so i know how you feel! Saying that though the last test you took is quite dark, i think you will get a positive in the next few days! I think miscarriages/chemicals can mess with things for sure so that may be why its taking a bit longer. Fingers crossed you get a good positive soon x
So sorry to hear about your loss x
That one above is definitely positive maybe you caugh it just at the end, I would go with ovulation around 24 hours after that positive x