She might be in some discomfort. Look for signs of teething, she could be gassy. Perhaps there is some material that is making her itchy or too hot.
We gave our daughter Gripe juice to alleviate her stomach aches and Orajel to soothe her teething pains. When they're teething they will be putting their fingers in their mouths, bite, drool a lot more than usual.
Another trick to sooth a stomach ache is to place your baby on your lap, on their tummy and rub their back. Put a towel underneath, as they tend to spit up that way.
Other reasons could be a change in temperature, it is her first spring. Noisier nights. Too much stimulation. Not enough stimulation throughout the day. Not enough darkness, or perhaps too dark. A change in routine. Even a parents routine change can affect them.
Sometimes you just gotta think back to when the last time she slept through the night and the first time she had trouble and look for clues. If it's nothing you can pinpoint, then it may be internal. It could also be growing pains. Try giving her a massage and see if that helps, too.
When I was in Lamaze, the instructor told us of a time when her little guy wouldn't stop crying no matter what they tried. It turned out that a piece of thread in his sock had gotten loose and was stretched between his toes causing pain.
