Changing the formula too much can easily upset your baby's stomach as they are really sensitive. However, it is important to find formula that doesn't show problems when fed to your child like a rash or irregular stool. You can consult a doctor to be advised on what to do in the situation for your child to feed well. Read more details at www.livestrong.com/article/487832-how-to-tell-if-formula-is-upsetting-my-baby/.
Colicky babies have immature digestion. (Breast is best for 3-4 months during this 4th trimester period.) however if not breast " Good starts" by gerber for colicky newborn babies is excellent . Gripe water right after feeding helps a lot as do gas drops, both over counter and approved by pediatricians, but it's the immature system that just needs time to develop and it's very hard on the parent. Burp the baby before during and after feeding and one burb is often not enough. Hold baby more upright so bubbles rise when feeding and burb in between feelings as well when not sleeping. Change the bottle to one designed for colic so no extra air is getting in. These thing are no cure because time is the cure, but they help.