URGENT - Colonoscopy Prep

I was told to do Miralax/Gatorade and Dulcolax laxatives for colonoscopy prep. I have IBS with constipation. How long will it take for this prep to start working? I have a hard time with preps as they do not seem to work on me the same way as they do others like 3 times as long to take effect as a normal person. Is this because the constipation? I use polyethylene glycol on a daily basis and have BM's. But since I cannot use that for a week prior to the procedure I am very worried about the timeframe for prep. Should I begin it two days prior so I am sure it works? Should I double up on the amount of Dulcolax they told me to take? They told me to take two and the last time I did that it had no effect whatsoever.

Hey Ocean, Miralax IS actually polyethylene glycol that is formed into a compound to use as a laxative. I don't know if you are using the ethyl gly strait from the bottle as if you were pouring it into the radiator or what? because other than Miralax, I've never heard of using it for any laxative. If you are doing that then be careful because it is very toxic and can kill you. BUT since you are taking it every day, then you most likely have built up a tolerance to it. I've had 2 colonoscopies done and the first doctor used the Miralax. I remember I did have to take much more than the usual amount on the first dose and had to continue it several times in smaller doses. I don't recall what the exact measurements were but I do remember it was way more than the usual. Also, he told me to take an enema if necessary. The fleet enema also has a laxative in it. On my second colonoscopy, my other doc gave me a prescription called Super Bowel Prep Kit. I get constipation too because I take pain meds and this stuff worked but I actually took double on the first dose by accident though it worked good. I was cleared out in 3 trips to the bathroom and excreting clear water in an hour. It lasted about 3 to 4 hours clearing the water out and finally stopped. If you think that the Miralax won't work, maybe he will call in a script of it for you. I got mine at Rite Aid and cost about 30 bucks. Also drink plenty of water a couple of days before you start the prep if you don't want to cut down on food as mentioned above on the other post.
Yes..and liquid diet starting when you wake in the morning of the prep.