Is it permissible for me to pray after the forty days of postpartum bleeding have ended and a continuous flow of red blood is still present, with uncertainty regarding the timing of my menstrual period?

This blood is considered nifas (post-natal bleeding) according to the Shafi'i and Maliki schools (where the maximum period for nifas is 60 days), and istihadah (non-menstrual vaginal bleeding) according to the Hanbali school (where the maximum period for nifas is 40 days), unless it coincides with the usual period of her menstruation.

Considering the returning blood as hayd (menstruation) is a valid and strongly supported opinion in terms of evidence.

If the blood is istihadah, one must perform what a woman experiencing istihadah does.

If the blood is hayd, one must abstain from prayer and fasting until it stops or until its duration exceeds 15 days, in which case you become a mustahadah.