Schulze's cleanses are very very good, but also very powerful. He has used them to 'cure' cancer and a host of other life threatening condition (including his own). The cramping does sound like a reaction to the senna or Cascara as they are designed to cause (mild) peristalsis.
I would switch to another weaker herbal formula, it may be that either you arent ready for the herbs, arent taking them correctly, have a dietary deficiency or that they are too strong for you.
I would still try Schulze's formula 2 though, if you have it. You may never even need one and could try the weaker Formula 3 instead. It will be interesting to see what condition your bowels are in, if they respond so dramatically. But personally, for now, I wouldnt continue with the IF1, that level of pain is not concomitant with healing.