FRER digital question...

Angel
So yesterday (11dpo) I got my bfp with a FRER line test and on a clear blue digital. Then this morning (12dpo) I took a FRER digital and it said NO-... So this afternoon after work I took another FRER digital and it still said No- and I took another FRER line test and the line was a bit darker then yesterday's test. So my question is has anyone else experienced this?? Help!! So confused!!