As far as i can tell, you may be mixing two stories. The las two scenes you describe, are most definately from Bound to Love By Blood by Brandypandyxxx
www.fanfiction.net/s/5097375/1/Bound-To-Love-By-Blood
Rated M on FFN
It may be on dokuga as well, but its bookmarked for me On FFN
your fisrt three scenes arent part of that story (well, at least not the way you described them). But it does involve a demon baby, that is given into kagome's care (not found beside a dead mother, because he doesnt have one. He is a pure blood demon. Sesshomaru basically created him). Sesshomaru eventually travels with the group for the child's sake (not necessarily to share his aura, but because he is the father). Instead of the baby constantly crying, they are actually a little worried because he NEVER makes a sound
Kagome is sent through the well, sesshomaru is left to raise the child, and eventually when she comes back, he says "mother" and races to the well to meet her.
This is actually one of my favorites, and i think im going to go read it again!