Gas pains?

How do you know your little one is suffering from gas pains?? My LO is 3 weeks tomorrow and formula fed. She’s been a great sleeping up until yesterday and she won’t sleep longer than 15/20min. She’s always struggled with pooping, but it’s never been firm and always mushy. She’s been super gasy and has been cluster feeding every 1.5 hours and only eating 1oz whereas before she would eat 2/3 ounces every 3 hours. I just feel like I can’t comfort her and I’m not sure if it’s normal to have these episodes or gas pains?