Everything starts out wonderfully. You have a brand new baby who is absolutely adorable. And then IT happens. Around three weeks of age, he starts screaming and there is nothing you can really do to help him calm down. This screaming can last for hours and usually happens at the same time of day every day. Both you and your baby are very stressed. Unfortunately, it sounds like you have a colicky baby.
Colic will rear it's ugly head in about 25% of all newborns and the causes can be very varied, from immature nervous system to an immature digestive system. The colic will slowly disappear, usually around the age of three months, but the time between three weeks and three months can cause many tears and much stress for both the baby and the parents.
For the formula fed baby, a main cause of colic can be a sensitivity to the protein in cow's milk or, in fewer cases, the sugar in milk based formulas. The baby may not have enough of the enzyme required to break down milk protein which results in a build up of gas in the intestines. This build up can cause the intestines to go into painful spasms.
If you formula feed, there are some steps you can take to help alleviate the colic. Many times changing the type of formula you are giving your baby can make a dramatic change.
Be sure to keep the communication with your pediatrician open during this colic period. She will be able to make sure that cause for the colic type behaviors is not a more serious illness.
Please note: It can take up to a week for the formulas to create a change in your baby. Rapidly changing from one formula to another will most likely create a temporary situation where the colic is worse, not better. Also know, that there may be a day or two where the colic seems worse instead of better while your child's system gets used to the new formula.
One of the first formulas you can try on your quest for a less colicky baby is Carnation Good Start. This formula has "Comfort Proteins" and the proteins are then broken down into smaller pieces, within the formula, to be easier to digest in baby's’ stomach. 
If you baby has a true sensitivity/allergy to the proteins in cow's milk then the particular formula will not be effective. Either your baby will be much better after you start using this formula or the screaming will get much worse. Unfortunately there is no real way of telling which result you will have until you try it.
The next step on the formula trail is to move onto soy based formulas. This may work for some babies, but about half of the infants that are allergic to cow's milk will also have a reaction to the proteins found in soy based formulas.
If the above formula changes don't work for your baby, there is a third type of formula to try. Hypo allergenic formulas like Nutramigen and Alimentum can make a huge dent in the colic symptoms. The major down side of these formulas is the cost. A can of Nutramigen can cost around $22.00, very expensive but well worth if it helps calm the colic.
In an attempt to defray some of the cost of these formulas, it is highly recommended that you sign up for their mailing lists. They send coupons out every so often that can make a substantial difference in the cost of a can of the formula.
Another suggestion is to buy the formula in bulk. A store, like Babys-R-Us, sells Nutramigen in a case and the cost comes out to about $3 less a can.
If you meet the income requirements, you may be able to get this formula through WIC, a Federal grant program. You need to check it the WIC offices in your state and you may have to get your pediatrician to write a prescription for Nutramigen,because WIC will most likely provide Carnation Good Start otherwise.
