Poop help needed

My little one is 6 weeks old. She is on breast milk and supplementing with formula enfamil gentlease (60/40 ratio of breast milk to formula) she gets about 3-4 bottles of formula mostly before bed and in the evening. Yesterday she wash grunting so much and straining that when I looked her stool was very formed like an adults. Once she pushed those few pieces out the  rest of the stool was the consistency of peanut butter (which is her normal) and dark green and brown in color ( which it has been for the past week or so) but why was her stool so hard?  I haven't been drinking enough water myself does that play a major role? Throughout the day she still seemed fussy and acted like she had a belly ache as if she needed to have another bowel movement. Her belly was not hard though.  I gave her an oz of prune/apple juice in hopes it would soften her stool if she needed to go again but it  still hasn't produced that second bowel movement. Any insight would be great as to her hard stool