As others have said it could be a lot of different things, my other half got ill about 12 years ago now, she has had a million test and they still don't know whats wrong with her. Its stomach/bowel related and a gluten free diet has helped her a lot although she is not alergic to wheat or coeliac according to the experts. They think it might be some sort of parasyte or a problem with her stomach acid. She still gets ill from time to time but its not really too serious and only lasts a few hours at a time.
In your case it could be a million different things, the human body is very complex, My thoughts are with you both, I hope its not something serious.