Google second night syndrome. It lasted more than one night for us regarding the night time, but it explained a lot. Again, he is just 3 days old, probably just adjusting, u got this ☺️
Completely normal, just adjusting to the outside world. He's not constipated, it's just that the meconium would have cleared his system now and his bowels are adjusting
look up newborn poop chart. And let him sleep on you send get the boob as much as possible
He's only 3 days old. He's probably adjusting to his new world, lots of cuddles and let him sleep on you. It's also common that babies poo will be irregular in their first week, GP probably won't do anything about that until it's been 48-72 hrs that he hasn't poo'd x