Strong letdown / 5 weeks old

Hi guys! Reaching out if anyone has any suggestions. My little one is having a hard time staying on because I have a strong letdown. 3-4 minutes in he starts choking and doesn’t want to eat anymore. He gets sleepy then wakes up 45 minutes later hungry again. I tried pumping a little first so it’s not as overwhelming for him, but then I feel like I’m only pumping my foremilk.

I am trying to space his feedings out to a minimum of 2 hours but I am having a really hard time.

Also, Is it too early to start sleep training? I am starting to read babywise.