My baby is 2 weeks old and is bottle fed, but we have been having problems from the start with constipation, stomach cramps, reflux etc, we think it's the formula. she is also constantly hungry like the formula doesn't feed her enough,her tummy hard?

Common: Infants have flabby/loose belly muscles & often need their breathing/fussing muscles to move food along or out. When they use them the tummy is hard. Effort toes not equate to constipation, dry, pellet like stools do. Babies also reflux & like to suck a lot as normal reflexes. You can try other formulas but I doubt it will change much.