Period day after ovulating

Hello ladies,
I've been TTC for about 6months now and I am using ovulation tests to be sure of my fertile window. For the last 3months I got my period the day after the test said I was ovulating, so I did not even have 48h fertile window, which is pretty frustrating. Even in one occasion I got my period the same day that the test said I was ovulating... Other than that my cycles are normal and fairly "regular". 
I have already scheduled a doctor appointment but I was wondering if somebody else has gone through the same and knew any reason why this happened because it's driving me nuts. Thank you