K.A.
It was different after each of my 3. My third was the worst, for the 6 weeks after she was born my body kept trying to start my periods back up and at 6 weeks I had a full and proper period. They kept up semi-regular until they went completely crazy and it now looks like at the age of 43 I am in menopause, this Sept will be a full year of no periods. My other 2 it was probably around 6 or 7 months before I started getting periods back, it might have been a little longer with my second. I got pregnant with my second and third children as well as one I miscarried between them all while still breastfeeding their older sibling.
All 3 were exclusively breastfed, no bottles, no pumping, no pacifiers, on demand day and night. Nothing different beyond what my body decided to do.
Every women is different and each pregnancy can be different.
I suggest putting away all the tests and just enjoy the trying and it'll happen soon enough.