Why did this happen after having my child?

Well, your milk did come in, that's why the size went from a 34DD, up to whatever size they were during/after pregnancy, back down to a 34DD. The spaciness of your boobs and the lack of cleavage is probably the result of having larger boobs at one point. You could get a push-up bra for cleavage, and eventually surgery (if it realllllly needs to come to that) But after having children, a woman's breasts will never look or feel the same as pre-child.