Disappearing positive

Ted

Took this this morning, pretty hardcore positive for the first 5 minutes. Followed the instructions to a T. After about 10 mins, we couldn’t see anything anymore:(. It’s been an hour now, pretty sure it’s just an evap at this point... but I see a faint line. Much more faint than earlier. This is what the invert looks like. Please give your opinions/ experiences. This is a Walmart 88 cent cheapie. This has never happened with this brand or any other before. I’m also pretty irregular, but guessing I’m at least 15 DPO. As I usually get my period about 12 days late. This app says I’m 18 days late. IDEK 🤷🏻‍♀️