Need help understanding my hpts!!

Today i am 15dpo. I had 3 bfp 3 days in a row(11dpo, 12dpo, 13dpo) with first response. Then 2 days in a row(14dpo & 15dpo) of first response negative digital tests. 3 hours after taking the digital hpt test at 15pdo( today) i took a first response non-digital test again and got a positive line, it is fainter than 11,12,13 dpo but it is still there. AF was supposed to be due yesterday and she has not yet showed her ugly face. I do have a Dr appt in 2 days time but i want to know if this has happened to anyone else and what it resulted in? Thanks.

Ps. I got angry and threw 1 digital test(from yesterday at 14dpo) in the garbage so i only have 1 to show haha.