Please help

I had my son 4 days ago. Breastfeeding went well at the hospital I thought. Since getting home it's been more difficult. My milk came in last night and there's so much I'm leaking. My son does not seem to be getting fed enough. I nurse him every 3 hours. He nursed for long but doesn't burp, he has not been peeing or pooping and is so upset each time. He seems to get enough, detached and goes to sleep but then within a few minutes is screaming like he's starving. I'm so confused what I am doing wrong. I am overwhelmed and I feel like w failure. I have to call the dr tomorrow because he is clearly not eating enough. What do I do