21 days old baby

There are many reasons why newborn keep crying and can't sleep well at night. One of the main reason is gassy stomach. You can try use swaddle (important and effective, make sure room ventilation is good, baby don't like if it's too hot), carry him near to your body and swing him to make him sleep. If you're unsure of the reason, you can bring him to doctor. They will prescribe ridwind and probiotic (biogaia) if baby diagnosed with colic. After bath you can massage his stomach and feet to expel the wind. Other reasons could be feeling insecure to the new environment, need change or hungry. Remember to burp baby after every feeding. Some baby need to burp a few times before you put them down.

6 to 7hrs sounds shag.