Aww mama, ganyan talaga ang 4-month-olds sometimes, it's such a tough phase! A few of us went through the same thing, and honestly it could be anything from colic, gas, or just overtiredness (gabi kasi sobrang stimulated na sila the whole day). Try mo muna mag-burp properly after feeds, or check if comfortable ang position nya while sleeping, pero since it's constant, better to check with your pediatrician para ma-rule out kung may physical discomfort siya or if it's just a phase. Hang in there, you're doing great!