Ovulation

Is it possible to ovulate while on your period? Af started the 24th and I started testing right before it started. It was pretty dark. I stopped testing till the 26 and when I tested the line was almost as dark as the control line but it wasn't darker.. Now everyday since it has gotten lighter. Glow says that I'm starting my fertile week today and that my ovulation day is the 3rd but today my test line is very very faint almost not there. I'm so confused!! This month is my first month using opks.