A little insight here??

Megan • Just wife and mom of 2 amazing kiddos she`s 12 and 11. Ttc number 3 since 2008 with PCOS & hypothyroidism.
So, glow says my period is due in 8 days. But that's wrong, I'm only on CD 15... I'm pretty sure I'm ovulating, or getting really close because I have had some cramping, and my CM is stretchy, but is it normal to have some old blood mixed in? I have Pcos and am on metformin if any of that matters.