Any advice? Tests not getting darker.. rainbow?

I had a miscarriage at 10 weeks and had a D&C on 9/9/19. My doctor had me do weekly hcg draws until they went all the way back down to 0. On 10/14 they told me my level was 0 and I started my period the next day. I tracked everything and ovulation and everything was normal. I started getting faint lines on 11/14. I've taken 10 tests since then and they all look the same. I've even tried 4 different brands. Period is due today and no signs of it coming. Any advice? Why aren't the lines changing at all?