fussy baby

Just curious if anyone else is having or has had the same concern?  Typically she isn't fussy during the day but she gets fussy in the evening (which isn't terrible) but the worst is when she wakes for her overnight feeding. She doesn't empty both breaststroke so I end up usually having to pump.  The problem is she eats and then is up for two or so hours just fussing and crying. She will settle for brief periods but not long enough to go back to sleep and then start in again. In the beginning I assumed it was gas so we do lots of burping but it doesn't seem to help.  Anyone have suggestions???