I just had a colonoscopy on Monday, I had a large polyp removed, and I had no problems at all.
I know it's been a few days since you posted, but I hope you called your Dr and reported these problems.
Good luck, I hope all is well and this is something that passed quickly for you.
I've not had my colonoscopy yet, but since I've tested positive for fecal occult blood I've got one coming up soon.
I did have an IVP a few years ago where I had to take the prep and had similar symptoms like you describe. After the test I had "dumping" where whenever I ate anything I had almost immediate watery diarrhea afterwards. After a couple of days of this I took Kaopectate and then became horribly constipated and ended up having to digitally disimpact myself. Needless to say it was a miserable experience. My bowels finally went back to normal but it took a while and I'm dreading the prep this time around.
For my colonoscopy I used a prep called "Movi Prep" while it wasn't the most pleasant experience, it seemed to be much easier than the prep my husband used when he had his colonoscopy. He used the prep that you buy over the counter at the drug store made by Fleet. (can't remember the name)
This is by prescription and it took the drug store a day or so to get because they had to order it.
It didn't taste very good, kind of like lemon Alka Seltzer, but it wasn't as bad as I've heard other preps taste.
Good luck with your procedure.