Colonoscopy and IBS

I have had IBS-D for four years..I have never had a colonscopy, but my symptoms were so classic that it was an wasy diagnosis for my family doc...well I just can;t take it anymore, so I finally bit the bullet and went to a gastro doc.  He was very nice and he too said classic IBS..he said I didn;t need a colonscopy because I had IBS, he said I needed it because of my age..
I told him that there was no way I could drink that gallon of whatever it is, I would be sick as a dog...he told me that I could use miralax and gatorade and it would be fine..I mean really I got the bathroom anywhere from 2 to 7 times a day, the prep is all I need to push me over the top...so I am hoping that I will be able to tolerate the prep and the colonoscopy will go fine.
A couple of other things, I do take things over the counter to attempt to slow down this condition..he suggested that I take fiber (which I already do) eat 2 cartons of Activia a day, take Beano (I don;t know why as gas is not a problem but I do have certain trigger foods...and also take a probiotic - (I told him that I had already taken them and they did not work, he asked me to try it again....he also suggested a blood test or endoscopy for Crones disease just as a precaution or to difinitivly rule it out.He wants me come back in two weeks to see if there has been any change....then we will schedule the colonscopy.
One other thing he did say was that even if he saw nothing in my colon he would still do a couple of biopsy's, I have been thinking about that, I should have asked him why, but I did not.
Hopefully, I can tolerate the prep, I can;t even imagine going through anything worse than what I do everyday.
Can anyone comment and any of these issues....and if anyone has done this particular prep I would like to hear how your made out.....I some info on the miralax prep, but it all said there were pills involved as well, but he did not say anything about pills, just 64 oz of gatorade and I believe he said 8 scoops of the miralax.
Thanks for any information that anyone can give me...I have put this off much to long, but honestly I still don;t think I can handle it..

Roe