I'd be suspecting kidney pain as well or perhaps another one of your internal organs doing some house cleaning.
I dont feel that it's bad, especially if you only feel the pain when on a cleanse. To me that suggests that the body is only getting a chance to work on it whle you're cleaning.
You should be sure to drink lots of additional fluids, and try getting the area worked on. I can't recommend enough how beneficial a massage (especial a visceral stomach massage) can be to your system during this.
I'd just trust that your body is working to heal. I get all sorts of interesting pains when I cleanse, and with a little body work, the pains go away and I feel so much better in the end.