Still no postpartum period!

I'm 13 months postpartum and I still haven't gotten my period! (Not that I'm complaining!!) I know I'm ovulating because I've taken the tests. But my husband and I are trying to conceive so I just keep taking a pregnancy test each month because it's the only way for me to know. (I don't have the benefit of a late/missed period to tell me if I'm pregnant!) Anyone else TTC without a period? I should also mention, I'm still breastfeeding.. a lot! My daughter eats food, but she relies on nursing as her main source of nourishment.