question about formula

My baby has been using the similac sensitive and does great on it. I just recently swapped to using the parents choice sensitive because they say it's the same thing just way cheaper. Well within the last 2 weeks I've noticed my baby getting constipated and he's never had that trouble so do y'all thinks it's cause of the new formula? Should I swap back to the similac kind? What can I do for constipation? My baby is only 10 weeks old.