I think Delhi belly is used as a general term for diarrhea in India. Diarrhea and upset stomachs can be caused by poor hygiene, new foods, or other causes.

I had a very bad case of Delhi belly a few years ago. The culprit: coconut oil. It most certainly was not poor hygeine, as the meals were prepared in a very clean kitchen.

The other people travelling with me were unaffected.

I suggest packing immodium or pepto bismol. Also, yogurts/raita have a soothing effect on my stomach. Consider eating good amounts of them if they have the same effect with you.