college dtr. with gastic symptoms

My dtr.( almost 20) is returning from college and states for the past 2 months she has had almost consistent loose watery stools usually soon after eating.  Sometimes loose sometimes more liake diarrhea.  She cannot associate with any particular food or event.  This morning she awoke nauseated and vomited X3 - green - yellow bitter fluid.  
She also stated that at one point a month ago she had very very dark stool almost black. She maintains a relatively healthy diet and no red meat.
What could we be looking at?
thank you

[Ratnakar Kini, MD]

Hi Mom648,
It could be infective colitis.
A stool examination may provide some clue.
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The information provided is for patients’ education only and is not a medical advice. Always consult your personal physician for complete evaluation of your health problem.

- Ratnakar Kini M.D.