Pain

In the last few days, I have felt a tight pain in [I think] my stomach, or that general area.  I can't pin-point what it is.  
I have been having kidney issues.
I get Migraines so I have taken Zapain [codeine] for the pain, several hours later, I felt the stomach pain again.
Today, after eating I admit a fair amount, I got that pain.
I have been thirsty and tired of late, which is nothing new as such, but I've been more conscious of it.
I believe I have Nephrotic Syndrome due to heavy frothing of my urine.
I am due a colonoscopy as an investigation into a couple of episodes of red blood on the stool.

Can you help with what the stomach pain might be and any other general comments/observations?

Thank you...