Question about faint lines, please help?

Lovely • IG: TTC #4. Sept 2014 tubal reversal. Feb 2016 HSG: blocked tubes. May 2016 IVF: failed. Aug 2016 BFP turned to 4th loss
I started getting faint lines 3/1 I tested today and its still faint maybe a little difference but not much. My af is due tomorrow, my question is shouldn't they be getting darker already? Any of you go with fading lines for days before there was a change? Should I be worried about chemical pregnancy?