Not medical advice...but I had a bug or something a few weeks back and that led to my seeing multiple articles/ reports of the benefits of macaroons...the coconut type. Perhaps I was already on the mend, or maybe it was the benefit of the coconut...but I picked up a pack at Aldi's and was eating one a day...and things improved...Sounds like you have more to explore though with this situation...
Our doctor was able to make suggestions on foods to avoid, foods to add and meds that might help. But these were suggestions after a medical work up. My husband is doing much better now.
Start with getting your father to a doctor for a check up. We on this forum are not physicians. Has your father been diagnosed with anything gastrointestinal in nature? If not then he needs a work up. Good luck!
If not then he needs a work up.
Good luck!