Second line developed next day?!?!

AB
So I know I can clearly see the second line on the test, however when I took this last night - no line showed up at all...so I figured the test was faulty. Then this morning I looked and there's two lines?! AF is due today and I haven't started yet. Went and took a couple 1$ store tests and both were negative...has anyone had this happen before with their first response changing on them?!