Would be happy to help you on this . Need some additional information though.
Does this wake you up from sleep in the middle of night too?
Any weight loss ? Have you been tested for parasite infestation e.g giardiasis ? Its usually tested with the help of stool tests for ova / cysts. Have you had your thyroid functions tested ?
Both parasitic infestation and hyperactive thyroid should be ruled out in your case.
What have you been prescribed for cramps ? Mebeverine is very effective remedy to these IBS cramps so you can take that thrice a day.
If your symptoms are not improving after all dietary modifications and mebeverine then adding imipramine ,or amitriptyline in low dose is the recommended next step.
Bear in mind that diet is the most important part of controlling or minimizing your IBS symptoms so pay special attention to the advice given in this link ;
In absence of weight loss , night time symptoms , blood in stool colonoscopy shouldnt be necessary.
I hope you find this helpful.
Let me know if you have any further queries.