so my daughter is 3 1/2 months old and she's been having these screaming fits. its like she'll be…

so my daughter is 3 1/2 months old and she's been having these screaming fits. its like she'll be fine one minute and then by the next she's screaming. I can normally get her to calm down rather quickly but lately she's just doesn't calm down like she used to. I pick her up and try to feed her or rock her or anything and she just Cry's until she falls asleep again. Has anyone else every gone through something like this with there baby?