You should get checked for gluten intolerance and/or Celiac Disease. Most people don't know that breads and pastas can be causing their stomach problems. It's actually very common, just underdiagnosed. And don't think that just because your blood tests come up negative this isn't the problem. You can be gluten intolerant and not have any kind of blood work abnormality.
any abdominal pain should be taken seriously i would go in and see a doctor about it. the nausia and diarreah may be a sign of an underlying condition
may be something your stomach is not accepting the food which you are having in dinner , may be that why your are having diarrhea and nausea, i also have this when i eat just before going to be or something heavy that lead me to diarrhea, but better seeing the doctor if concerned . Good luck