What Causes Lower Abdominal Pain With Diarrhea?

68 yo male good shape lower abdominal pain, day 2 - day 1 diffuse below navel, mild lower back pain and headache and normal mild arthriitic joints (not flu like symptoms) no new foods, core exercises,no vomiting or diarrhea, passing urine and stool albeit small amount of stool and reasonably hard -- normal with higher protein diet. slightly better and lower pain day 2 - still diffuse, milk of magnesia 2 oz at 7 and 3 oz (day 1) -- some diarrhea 2 am and 5 am. Day 2 still pain slightly lower and maybe more to right side 4pm - day 2. Little food and does not heart abdominal muscles to strain for defecation but very small yield. Hurts 5-6 with cough