Conditions General Question about hunching up

[Demiba]

Hi, Just took my piggy to the vet yesterday because she was hunching up and whimpering a bit when pooing. Xrays were taken and no stones, and she is eating and drinking normally, happily stuffing her face with hay. Now she is fine. This happened in January also. Any ideas? I wonder if her water was off somehow in taste and she drank less so was having a hard time passing poops? They are normal looking. Thank you!