Line on tests but never pregnant

Soo I have being ttc for 5 months now... and I have taken first response tests quite a few times. The first month of trying no lines nothing, but the second month I got quite a few lines, vvvf but could still see but got period. So I decided to stop testing altogether and this month I decided to test again on period due day as it hadnt come yet so I took a test and a faint hut clear line come up instantly so I thought it was the start of something just for my period to start a few hours later.

Does anyone know whats wrong with first response tests? Its very heart breaking that I really want a baby and trying but these tests are always giving me lines but then i get my period.

As anyone else experienced this?