What Causes Pain In The Abdomen That Radiates Towards The Rectum?

I am 66 yrs old and good health I am not on any meds. But I am experiencing stomach pains starting from the lower part of my stomach and endig sometimes through out my colon and ends at my rectom. My Tongue feels dry and Im drinking extra water.Its lasting a week now and I am not constipated.Nor do I have loose stools.Occasionally I have a fever and bouts of tiredness. What do you think the problem is?