Pregnosis tests - false positives and evap lines

Hi, just wondering if this has happened to anyone else? Ive been googling pregnosis tests and it seems quite common to get either false positives or evap lines showing up.
AF is 2 days late, have used 4 tests over 3 days, the first 3 all showed invalid results (so no lines came up at all which i thought was really strange. They were first response and 1 pregnosis test). This morning tested again, control line came up straight away and then 2nd line after that. I cant get away to get more tests until tomorrow so driving myself crazy here. Wouldnt the "positive" line show up first if it was a true result?