Kabrita Goat

FTM with a 9-week-old looking for some advice. We recently switched from breast milk to Kabrita goat formula due to reflux/colic symptoms and needing to stop breastfeeding for my own mental health. Over the last 6 days he’s only had 2 bowel movements on his own, but in between he grunts, strains, and seems really uncomfortable like he needs to poop. On breast milk, he had poop every time his diaper was changed. He’s also been fussier and sometimes doesn’t want to eat as much when he seems backed up.

For those who’ve experienced this — should I stick with this formula and let his body adjust, or try another one? How long does it usually take for babies to adjust to a new formula, and does the straining/fussiness improve?