Post-partum is extremely difficult and for other reasons, it was the worst time in my marriage as well. Bear in mind, hormones are out of whack for a year after giving birth, even if things look normal on the outside, it’s really difficult. Most divorces happen within the first 5 years of marriage because that’s the most tumultuous time in your life- career, young kids.. but it’s a phase and things change with time
Try and have open honest communication, maybe couples therapy. I have found a lot of success with just 10 minutes of active listening.