Fussy while feeding?

My baby is 4 weeks old and she is very fussy at some feedings. I changed her bottles, i give her gripe water and this week i changed her formula with the doctors consent and she is still fussy. i changed her from Similac advanced to Enfamil gentlease w/ lipil. She pooped green yesterday and its usually yellow. Does anyone else experience this? Is it gas or colic? whats with the change of color of her poop? What should i do next?