Crying and feeding non stop.

Hi Mommies, I just given birth 6 days ago and a first time mom. During the evening my baby cries ALOT. Even after feeding and change of diapers he still cries. He would open his mouth and look like as if he is hungry even after i just breastfeed him for 20mins. He would also cry the moment we place him in his cot. He seems so fussy and not comfortable at night but he sleeps well (we will wake him up after 3.5hrs to feed) during the day. Any advice why baby cries, dont sleep and fuss alot at night?#pleasehelp #advicepls #1stimemom