Just skimmed this thread - Katy, I had a colonoscopy the same day you did, it wasn't much fun either.
Oldbag - not wanting to gain weight is a daft reason for not having steroids. I'm not being horrid, just honest - any weight gain is temporary, and the relief that steroids bring is HUGE. Seriously - I can't have them any more, but within a matter of a couple of days you could feel well.
The reason people gain weight is that they make you hungry, so you can control how you handle that. And, as Spiderlight says, there's no guarantee that they'll have any sort of effect on your weight anyway. I took 80mg a day for months, and didn't gain more than about 2lb.
Anyway - if you're having a full colonoscopy I'd do the picolax. It honestly won't be that bad based on what you're experiencing already (I took it last week, second dose sent me flying to the loo but seriously not painful, and over quite quickly). If you're having a sigmoidoscopy I probably wouldn't bother too much as it'll be clear enough for that without Picolax.
I hope everyone feels better, it's so miserable having anything that sends you rushing to the loo.
Oh, should have said - I have Crohns disease, had it for the last 8 years. I know quite a lot about both crohns and colitis, so happy to help if I can.