Positive lines not getting darker

Dye • EDD: 9/26/19 💗🎀 Geriatric pregnancy 😂 Second pregnancy although it feels brand new! 16 year old son 💪🏻💙

I have taken FRER and all (including the digital one) were positive. I’ve taken them for a few days and they aren’t getting darker. Should I be worried? Drs appt scheduled for next week