Please remember that this is a temporary problem. It is your depression speaking to you. It is not you. Try to tune out the negative voices causing these destructive thoughts.
You are not bad. You are a loving mother. But your brain chemistry is preventing you from being your true self. It is normal and common to feel this way.
About 30 years ago a woman in my city was going through what you are going through. She killed herself and her baby.
Post-partum depression was not so well understood then. Even though this mother was a doctor, she did not get the care she needed.
You are living in a more enlightened time. Tell your doctor you are feeling this way. You don't have to suffer alone. Tell your husband. Tell your parents. Tell a friend.
Do not keep this to yourself out of shame. You have nothing to be ashamed of.
You are going to be alright.