What cause a 7 week baby to pass to much gas and constipated?

There are 2 factors for passing gas. The air swallowed during feeds & gas produced by gut germs feeding on digestive debris. A breast fed baby can poop a smear every feed or a diaper filler once a week. If it is soft when they go it is not constipation.

Gas is from two sources- swallowed air and what is made during digestion. Suggest trying a non-cows milk formula. Also suggest experimenting with different nipples to try and decrease swallowed air.Sometimes a slower flow nipple is helpful. Once you make a change, give it 5-7 days to make improvements- these don't happen overnight...! Burp well and often during feeding...