Does your infant have a regular fussy period each day when it seems you can do nothing to comfort her?

This is quite common, particularly between 6:00 p.m. and midnight—just when you, too, are feeling tired from the day’s trials and tribulations. These periods of crankiness may feel like torture, especially if you have other demanding children or work to do, but fortunately they don’t last long. The length of this fussing usually peaks at about three hours a day by six weeks and then declines to one or two hours a day by three to four months. As long as the baby calms within a few hours and is relatively peaceful the rest of the day, there’s no reason for alarm.

If the crying does not stop, but intensifies and persists throughout the day or night, it may be caused by colic. About one-fifth of all babies develop colic, usually between the second and fourth weeks. They cry inconsolably, often screaming, extending or pulling up their legs, and passing gas. Their stomachs may be enlarged or distended with gas. The crying spells can occur around the clock, although they often become worse in the early evening.

What Causes Colic?

Unfortunately, there is no definite explanation for why this happens. Most often, colic means simply that the child is unusually sensitive to stimulation or cannot “self-console” or regulate his nervous system. (Also known as an immature nervous system.) As she matures, this inability to self-console—marked by constant crying—will improve. Generally this “colicky crying” will stop by three to four months, but it can last until six months of age. Sometimes, in breastfeeding babies, colic is a sign of sensitivity to a food in the mother’s diet. The discomfort is caused only rarely by sensitivity to milk protein in formula. Colicky behavior also may signal a medical problem, such as a hernia or some type of illness.

Although You Simply May Have to Wait It Out, Several Things Might Be Worth Trying:

• First, of course, consult your pediatrician to make sure that the crying is not related to any serious medical condition that may require treatment.Then ask him which of the following would be most helpful.
• If you’re nursing, you can try to eliminate milk products, caffeine, onions, cabbage, and any other potentially irritating foods from your own diet.
• If you’re feeding formula to your baby, talk with your pediatrician about a protein hydrolysate formula. If food sensitivity is causing the discomfort, the colic should decrease within a few days of these changes.
• Do not overfeed your baby, which could make her uncomfortable. In general, try to wait at least two to two and a half hours from the start of one feeding to the start of the next one.
• Walk your baby in a baby carrier to soothe her. The motion and body contact will reassure her, even if her discomfort persists.
• Rock her, run the vacuum in the next room, or place her where she can hear the clothes dryer, a fan or a white-noise machine. Steady rhythmic motion and a calming sound may help her fall asleep. However, be sure to never place your child on top of the washer/dryer.
• Introduce a pacifier. While some breastfed babies will actively refuse it, it will provide instant relief for others.
• Lay your baby tummy-down across your knees and gently rub her back. The pressure against her belly may help comfort her.
• Swaddle her in a large, thin blanket so that she feels secure and warm. 

When you’re feeling tense and anxious, have a family member or a friend look after the baby—and get out of the house. Even an hour or two away will help you maintain a positive attitude. No matter how impatient or angry you become, a baby should never be shaken. Shaking an infant hard can cause blindness, brain damage, or even death. Let your own doctor know if you are depressed or are having trouble dealing with your emotions, as she can recommend ways to help.

https://www.healthychildren.org/English/ages-stages/baby/crying-colic/Pages/Colic.aspx