Aw, napakahirap talaga yan, a few of us moms go through the same thing, lalo na around 3-4 months old. Usually it's either overtiredness (kasi babies can't regulate sleep nang maayos pa), gas, or sometimes ang gabi lang talaga ang fussy hour nila. Try mo yung classics: gentle rocking, swaddling if baby's still small, or dimming the lights 30 mins before bedtime, at if mayroon kang space, white noise or fan sound para ma-calm sila, life-saver talaga yan sa bahay namin. If umiiyak siya nang matagal kahit may feed, cuddles, at clean diaper, it might be reflux or colic, kaya better to check with your pedia just to be sure everything's okay.