My partner and I went to India some years ago (early 90s). He´d never been there. For me, it had been a lapse of some 20 years.
We took no vaccinations and were very lucky to return safe and sound!! Another time he was there (once again, no vaccinations), he came down with some bad stomach problems but a good homeopathic doctor took care of that. We were told eating coconuts - the soft skin-creme called "malai" meaning creme - as well as drinking the juice would be the BEST "medication" for any tummy-digestive problems. In fact the homeopathic docs there, are to be highly recommended. Ask around (pharmacy) for a good one, obviously some are better than others. Or Ayurvedic Docs - once again make sure you don´t go to a quack.
Avoid eating meat, salad and drinking the local water. Soft drinks as well. When in a restaurant and if ordering bottled water, make sure its opened by you and does´nt get served already opened. Otherwise indian food is DELICIOUS!
Enjoy your holiday!