I Am A 63 Year Old Male With A History

I am a 63 year old male with a history of kidney stones and prostate cancer. I completed radiation treatments in June of 2012 and have had good PSA numbers since. I also had a colonoscopy in 2012 in which 2 polyps were removed and tested that came back as benign, non-cancerous.
I been having varying levels of constant pain in the lower right side of my back for 2 weeks, which initially made me think it could be a kidney stone. More recently I've been having abdominal cramps along with gas and mild nausea, and the feeling like I frequently need to have a bowel movement. I still have a good appetite and have not noticed any blood in my stool or urine. What are your thoughts?