Eating too much?

I've been breastfeeding my son for 2 weeks. Sometimes he only eats for roughly 15 minutes to 30 minutes at a time, but tonight he ate for 20 something minutes and then turned around and ate again for 30 something minutes and then 50 minutes later, ate again for 30 minutes, after being EXTREMELY fussy that whole time.

I know he comfort nurses, but I wasn't sure if that's what this was. About 15 minutes after he ate, he spit up a lot - it was more like a little thick throw up. Then he had a big poop, and he has been sleeping soundly since.

Is that normal? I'm sure it is but he just seemed so puny and then after he got so calm, even during his diaper change.

I'm sure he may have just had a tummy ache or gas or something, but even though I've already had one kid and he is my second, I'm slightly freaking out and I just want to sit awake and watch him sleep because I don't want him to get sick again

It may be important to note that he has Hypothyroidism and breast milk jaundice.