Could this be irritable bowel.. Bentyl medication?

I have a severe pain in my upper right side, I was in the hospital for it. They said that the CT scan showed a thickening of the intestines, but that that's not uncommon and 9 out of 10 times the colonoscopy shows nothing. Could my IBS be causing this pain? I am in my early 20's and don't want a colonoscopy. I'm really worried about the pain, it's affecting my job, and life in general. Any advice? Also I was prescribed bentyl to see if it would help, anyone else on this, how long does it take to adjust to it? I'm constantly tired and don't feel "right" ? thanks!