Baby won't poop - constantly hungry

My 6 week old only poops about once a week. It's not hard poop so I don't think he's constipated. Daily, he screams and cries and and appears to be in pain with a hard tummy. The only thing that soothes him is eating. He drinks breastmilk and formula. We just switched to Gentlease by Enfamil about a week ago to see if that'd make him poo better. He pooped two days in a row when we first got it... nothing since.

We do daily probiotics and gripe water and gas drops. We've tried warm baths, skin to skin, massage, bicycling... Nothing seems to soothe him. He seems like he's in so much agony when he's crying. And he'll just want to eat and eat. Always acting massively starving. How can he eat and eat when he hasn't pooped in so long!?

Of course, I'll be checking in with my pedi today since the formula switch hasn't helped yet. Just wondering if anyone else has gone through this? What worked?