Is my baby constipated?

My baby strains all day and today when she pooped it was firm. Like it was hard to wipe her but firm. She’s never had this poop before and I’m a first time mom so I’m not sure if her stool is changing since she’s getting older or what. S he’s only 4 months old. She’s never had firm poop. She’s on similac alimentum which she’s been on since she was a month old. Later during the day she pooped again and it was a lot more lose and I noticed tiny black specs, a couple days ago it was seedy. She’s always pooped once a day since she’s been born. No change in diet. She takes liquid form omeperzole for her reflux which she’s been on for 2 months. We did decrease her dose two weeks ago and ended up going back to her regular dose since her reflux symptoms got worse. Is her poop okay? I hate seeing her strain so much :(