Oh boy! We've all been there.  The agonising wait for the first appointment, then the agonising wait to have a test, then the even more agonising wait for the result.  I think the vast majority of the members of this forum know exactly what you're going through.  You probably know this, but not eating and not sleeping don't help your situation in any way, so at least try to keep up your strength by eating. 

I've found this little video a useful way of keeping calm at times like this: How to meditate in a moment.

You don't need to watch the whole thing (5 minutes) each time; on your second and subsequent go you can skip ahead to the part with the timed meditation. 

I don't know if it's any consolation, but with a colonoscopy you usually get the result at once, although if they take any biopsies then there will be some delay before those results come through. 

Best of luck - please tell us how you get on, both with the meditation and the colonoscopy - and any other way you might find of keeping calm.