Baby is in discomfort! How do you know?

RS

My son is 4 weeks today and every evening he is on cluster feed from 9pm to 11pm. Yesterday, he was fighting sleep from 8pm to 1am. He was not ready to close his eyes, not crying, super calm and playing but not closing eyes. Just passing gas(like normal, not alot) Seems overtired.

After 5 hours I decided to give him gripe water, in case if anything bothers him. And he goes to sleep after 5 mins.

I’m super confused now, what are the signs that shows baby is in discomfort?

My first cry her lungs out when she was gassy/constipated or anything. But this baby just don’t cry 😢