Oh you poor thing . It's so hard when they just cry and cry.

Like Tracey said, I would look into reflux. Also, have you tried something like Infacol? I found it worked wonders with my DS when he was screaming with wind pain. Do you have a paediatrician you could take her to? A friend had a screaming baby for 6 months and it turned out she had a UTI that was only detected at the children's hospital. I took my unsettled babies to a paediactric chiropractor and found out they had problems (one had a dislocated shoulder from birth that wasn't detected) and the chiro fixed them up and they were much more settled.

Sorry, just throwing lots of theories at you, I'm not much help!