Fussy fed Baby and Mum with bad Indigestion?

I have a very fussy 4 month old. She is fed on demand and is constantly crying and fussy during the day. My digestive system is terrible at the moment (diarrhea, wind etc) and I wondered if the two things are linked and if anyone has any similar experiences/suggestions. She is still gaining weight steadily and the Health Visitors are happy with her progress but I'd love her to be happier. I seem to be surrounded by mums who have chubby contented, formular fed babies too and that makes me feel sad for my little, fussy one!