It's still possible to experience a period while nursing. It's just not as likely. If it were the placenta you are at high risk of infection and need to see a doctor to check.
So now the cramping is gone and I think some tissue fragments have passed... thinking it was placenta tissue? When should the bleeding be done? Not a first period as I'm nursing and on the mini pill.
Its most likely your first period. Just take some tylenol.