My 3 week old just isn’t eating

My LO has had some tummy issues sense birth. He’s passed gas like an adult and has reflux but the gas hasn’t seemed to bother him at all. Yesterday he started crying with his tummy when he needed to pass gas so we started gas drops (recommended by or pediatrician) today he’s acting miserable and refuses to eat and just isn’t going through the normal with diapers. He’s being super clingy and just acting like milk is painful to drink. Tips? If he isn’t acting more like himself we’re going in first thing tomorrow.