Abdominal tenderness and bowel habits.

For about three months now I've been having mild abdominal pain, generalized and mostly tender on palpation, and cyclic bowel habits.  For 3-5 days I'll have fairly normal bowel movements, and the next I'll pass less stool or won't go at all; some days I'll go once and and a few more times after that, however, it seems my stool gets longer and thinner when my stomach is upset.  My stool isn't as big as it used to be, but I'm eating different and it's probably more normal for most people.  I don't have any blood in my stool and no diarrhea.  I've noticed some spasms in my abdomen.  Sometimes when I eat it doesn't take me much to get full and it's usually heavier foods. I haven't lost weight or my appetite and feel generally fine.  I'm 26 years old, and only family history of colon cancer is my grandmother.