Tell me what you can give a 4-month-old baby who clearly has stomach p…

Tell me what you can give a 4-month-old baby who clearly has stomach pain, is turning, and gets fussy from it or starts crying. They're being difficult, arching their back, and their chest isn't taking in milk. Every attempt at sleep for me is hellish, I have to rock them for an hour, although I never had such problems before. They sometimes have loose stools. I haven't given anything to their tummy before this. What can I buy? There's no free time at the pediatrician for the next while, so we need to do something now. I'm already in a panic.