lol yeah the old cluster feeding will send you mental, poor love's!
And yes, if you think about it, they're using their digestive system for the first time, so poop takes a little while to regulate. My little one had mild colic for the first few months, just make sure you burp him really well & cycle his legs back & forth to help move the trapped wind & get his poopies moving. Constipation can be very painful for them.
I remember in the first month, Sophie didn't poop for 5 days! I was beside myself, bought some gripe water, cycled her legs & the explosion that came forth was so exciting lololol
This may be the only time in your life, you get excited over poop