My son, 1month old, cries, pops out his eyes & cringes everytime before he passes yellow soft baby stools or passes gas. I’m breastfeeding, no solids yet.

Could be normal. Babies use their breathing muscle to help generate the pressure needed to poop. They don't sit upright or have developed abdominal wall muscles. If they fuss & cringe as part of it I don't assume they are in pain. If the kid is growing and having playful moments otherwise I would ignore it.