When / how did u know ur babe had acid reflux?

Just seeing when and how you ladies knew your baby had acid reflux? My four week old has started spitting up ALOT. Even a few hours after feedings. He is also more fussy like he’s not comfortable. His doctor said to get some gripe water to see if it helps and he needs to be seen. He’s going for his month check up in two days so we’re waiting it out and going to see if gripe water helps.