A constant crying baby?

hes nearly a month old and we've tried everything, feeding him he wont have a bottle, winding him but nothing is coming up, changed his nappy, talked to him that hasnt worked either, put him in his baby bouncer but he wont settle even tried him in the cot but he just screams and we have tried everything possible but nothings working for us anyone got any ideas what could be wrong and how to sort it thanks people