Constipated for 10 days and laxatives are ineffective. What to do/expect?

On Wednesday the 8th I used the bathroom and had a loose stool, upon wiping I had quite a bit of blood on the tissue paper. I was able to go once more the next morning, again with loose stool and blood. Now I can't pass my bowels whatsoever. I have gone to a gastronomy center and now I have a colonoscopy in 3 days. I've had x-rays ruling out obstruction but they see a lot of stool that needs out. Only problem is I cannot pass any stool which I'm told I need to do so for a good exam. I have been on Miralax for 4 days with no luck, tried a small enema with no luck and have been on a liquid diet as well. What do I do? I am going to be starting my prep (magnesium citrate) as well as surprep on monday. I am hoping these work but if not what do I do? Will they perform something to cleanse me? HELP?