Opk help!

Hi ladies! I was wondering if anyone else has had this problem. I’ll start off by saying that I have been ovulating and it’s been confirmed by my doctor. I’ve been taking opk’s since right after af stopped. Since then I’ve seen a clear and distinct line progression. I thought I was close to a positive test, but tonight I came home from work after a 3.5 hour hold and it produced a very negative, There’s almost no line at all. Could this just be that I didn’t have a long enough hold? I’m starting to worry that I didn’t get a positive test because I didn’t ovulate. I’ve had very strong positives each month before this as well. Today is cd 15 on Glo, 13 on Ovia (I compare both). Ovia said I shouldn’t ovulate until early next week. Glo on the other hand says I should ovulate tomorrow, but by the looks of this test it isn’t gonna happen. I historically ovulate between cd 18 and 20 with my earliest being 17. Would my opk’s be dark if I’m not ovulating for several more days? I’m just confused 😩 helpppp! He