My 3 months old baby cries out loud every day at night only before going to sleep all day he is active and feeds well what could be reason ?

Fatigue, anxiety: Babies at 3 months do get tired but do not understand the concept of sleep. They have enough memory to handle their wakeful periods, but really just pause between them.They do not seek or understand sleep until into their 2nd year. An illness or food reaction would cause fussiness all the time.This often improves as they pas 4-5 months and can roll over and entertain themselves more as they settle.