My fiance has been having stomach issues with uncomfortability and
Acute gastroenteritis most likely overlapped with prostatitis.
Hello and thanks for choosing 'Ask a doctor' service for your query,
I have gone through your query very carefully.
Very likely your fiancee is having a bacterial infection of gut along with inflammation of prostate gland which is very likely caused by infection of some strain of bacterium Escherichia Coli.
-A urine test and ultrasound of prostate gland to rule out bacterial infection and extent of inflammation in the prostate.
-Stool routine microscopy test.
Please tell your fiancee to drink plenty of fluids, oral rehydration solution and electrolyte-rich fluids like Gatorade.
Once the reports received, antibiotic therapy would be started accordingly.
Do take light food.
Please feel free to follow up with reports,
Hope I was helpful.