Baby spent a night with the grandparents. She did great during the day, but was extremely fussy in the evening and morning. The grandparents are insistent that she needs to change formula. She was fine the week prior (she would usually fuss for about an Hr around 7) but has been increasingly fussy since spending the night with them. Could it just be a growth spurt? She is on generic infant formula now, and gets some breast milk mixed in.