Allergic to formula?
Babies can be allergic to certain proteins in formula and breast milk. If they are you will see lots of forceful vomiting and they may have issues with not wanting to eat or eating too much due to stomach pains. They may also be very gassy and seem to be in pain if they can't release the gas. The biggest thing we noticed with my son was that his bowel movements were very loose and smelled terrible. No baby poop smells good, but this is another level of bad smells that I can't even describe. Unfortunately the loose bowels made him have a continual diaper rash as well.
If you suspect an allergy you may be able to try soy formula or a special formula like Alimentum.