When all else fails, try hydrocortisone (prescription)
Dove liquid body soap for sensitive skin. It is relatively cheap, and I use it to wash his body and his hair. I also use the Aveeno anti-itch and it really seems to help. When all else fails ask your peditritian for a prescription of hydrocortisone. There is also a new hydrating lotion by prescription only named Hylira. My ped gave us some samples, but it can sometimes make it worse which it did with my son. It could work for your baby though.