What Causes Stomach Cramping After Starting Zoloft?

My 17 year old daughter started Zoloft Friday and saw a decrease in her sadness within days. Today she has stomach cramps and was not able to sleep very well last night. I know there are sometimes side effects while a body adjusts to new medications. Is there something she should do to help alleviate the symptoms or is it something that will go away on its own once her body has adjusted?