There’s not a lot that actually passes through breastmilk aside from a few allergens like cows milk and soya etc It’s common for newborns for the first few months to struggle to poop. As long as it’s not hard they don’t have constipation they’re just learning how to poop!
Just cut soy, dairy and gluten. Those are the only things that really pass through. My son was colicky for the first 2 months but it wasnt my breastmilk like i thought, it was just he had a lot of gas and had trouble getting it out. Look up the I love you massage, bicycle legs, the superman hold and how to massage his feet for gas. Also could try pumping and putting it into anti colic bottles (this is what ultimately helped my son). People are quick to say its the breastmilk but most times babies that little just cant pass any gas by themselves
Honestly I don’t think it has much to do with your breastfeeding, my daughter is a 6 weeks old and she’s having trouble pooping so did my first around that time too!! Sometimes I help them out by sticking the thermometer into the bum bum with Vaseline to help pass gas, but I would only do that if I see they having a really hard time