Apart from UTI, what would be the reason for lower abdominal pain?

Hi doctor,

My husband is 28 years old. He has had lower abdominal pain since two months. I have marked the paining area in the attached picture. He has pain in the area just behind this in the back also. The pain is mild about 0.5 in 10 scale and sometimes 2 or 3 out of 10. There is a mild burning sensation while urinating. Previous medical history includes that he had diarrhea for about 25 days, out of which about one week was severe. He had about 85 times in a week and hospitalized. While in hospital, he had increased potassium (4.7) and was given a nebulizer for two days. On the discharge, potassium was 4.4 and they said it was normal. This happened two months ago and from the day of discharge, he has been normal. Last week, visited a urologist for UTI like symptoms. They checked urine sample and also took a blood sample. All other parameters were normal, except potassium which was 6.2. Later, it was 4.4 and doctor said some sampling error. I have attached his urine test report. Our doctor said there is no urinary tract infection.

What is causing this pain, if not UTI? We had US abdomen two months back during the diarrhea issue and it was normal. I have attached that reports too. This pain has been irritating though not disturbing his sleep. He sits for a long time in front of the computer for work and does no exercise or other physical activity. Would that be a reason? He travels a lot and has erratic sleep patterns. Though he has adequate sleep, he sleeps very late at night. Please share your opinion.