I'm wondering if this has anything to do with how hydrated you are? i.e. they say that the tests work better in the morning because your urine is more concentrated, right? Well, are you consuming more water in the evening/night time? That might make your FMU less concentrated, hence the negatives.
This must be so frustrating for you but try hang in there and distract yourself if you can. There's nothing you can do now but wait. I hope it's got a good outcome for you though and I'm keen to hear any updates. Best of luck!