4 week old crying for hours straight?

It seems like whenever my 4 week old is not sleeping he is crying, I hardly ever see him awake with out crying .. The other night I tried putting him in his binet and he cried for almost 3 hours straight , the only way i could get him to stop was to sleep with him, he also does not sleep alone he will only sleep if he is being held .. please help I tried gripe water and gas medicine I dont know what could be the problem and im getting worried.