Help! Fussy baby at night time.

My baby is a month old and starting at 3 weeks old she gets fussy every night around 9pm and will cry off and on for two hours. Sometimes she starts at midnight and doesn’t go to sleep until 2 am. I was starting to think it’s her stomach because she spits up a lot and cries and squirms. I also can hear her stomach making noises. The weird thing is she has breast milk all day only and she is fine all day never cries. So why does this only happen At night?

Any advice or what this could be??