LO admitted to the hospitol

My 3 week old has been super fussy these last couple days. Nothing I did soothed him. He wasn't eating, or sleeping, only cried. I took him to the dr and he sent me to the hospital for bloodwork. The blood work came back abnormal so we got admitted for a 48 hours antibiotic treatment for suspected infection.

The blood culture which confirms infection takes a few days to have the results. They came back this morning negative. So now they're saying he is fine, there's nothing wrong. Not that I'm glad my son doesn't have an infection, but it's discouraging that we don't know what is wrong. I can't help but feel he is hurting.

The nurses think he might have colic, but dr said no that he thinks the baby is just hungry and not getting enough from my breast milk. He suggests I supplement with formula.. I have supplemented the first weeks because he had bad jaundice and it was recommended I do so. This week I stopped formula and just 100% breast milk. He was born 8lbs and is 9 lbs 9 oz. So he's gaining healthy

I feel like the dr is just being lazy and doesn't want to look deeper into what is going on. Jot to mention he keeps calling my son a cry baby 😠 just frustrated and wish I knew what is happening with my son.