It's your thinking that's making you unhappy and probably what's affecting your sex life. It sounds like post-partum depression. Talking with a women's health professional of some kind will probably bring you some relief, some sense of normalcy, and maybe even a cure for what sounds like a hormonal imbalance common to women who have recently given birth.
I would talk to your ob/gyn (doctor that delivered your baby) about post partum depression. This is not uncommon after giving birth. And some women do have a let down sort of feeling. Life will never be the same. Your body will never be the same. But there is beauty in the changes once you've become a mother. However, it's not always easy to deal with. Between hormones shifting (affecting mood and libido) and possible depression/anxiety after the baby, please talk to your doctor. Mine very much wanted to hear about this and proactively asked me questions to try to uncover if it was going on because they want to address it with women rather than letting it get worse. So, give your OB/GYN or doctor a call. good luck