Doctors aren’t concerned?! Updated

My 3 month old has struggled with his stomach since he’s been born. He spits up/ throws up a lot, only weighs 10 pounds at 3 1/2 months.

Hes been spitting up this crap but the doctor isn’t concerned I’ve took him 10+ times and they do nothing.

What do y’all think I should do? I’m at a loss...

UPDATE: so I took him to the doctor this morning and he saw his normal pediatrician who did seem very concerned about the color. She put him on Zantac

These are all different days. No blood in poop