I was diagnosed with colitis when I was 11, and now I am 17. I haven't really had symptoms that I can remember since I was that age.
However, in the past month, I've had about 5 bloody stools, and when I spoke a few weeks ago (at that point I had 3) to my doctor, he said it prob. wasn't related to colitis but something blocking that area that was irritating it.
However, I went on vacation, and on Wednesday, I got a bad stomach ache. I assumed it was cramps, but it continued the next day and the next. on Friday, I wasn't able to pass a bowel movement (after thinking I had to) and when I wiped I came away with dark red blood.
I feel completely bloated now (and look it – I look pregnant or something), my stomach hurts, and I wish I could pass a bowel movement but can't.
I read that drinking carrot juice would help, so about an hour ago I drank a glass and a half, but nothing has happened.
I ate very lightly today – some pieces of fruit, a few raisins, airplane pretzels, airplane Wheat Thins, and now carrot juice.
Last few days before that I was eating normally (a few junk food items), though.
What can I do and how long will this last?? I'll be meeting with a doctor next week.
Extra info: I take 8 pills of Asacol a day.
I'm starting a new school on Tuesday, so I hate the fact that this came at a horrible time. 
How long does this last, and do you think it's related to colitis?
Don't listen to the guy talking about gluten. Gluten aggravates people with Celiac Disease, not colitis. my best friend has Celiac and is gluten free. I have tried it and it has not helped me, and my doctor tells me that Colitis is an autoimmune disorder and that foods don't cause it.
I have Colitis as well, and this definitely sounds like a flare up. Try eating soft foods, and stay away from spicy stuff because it can feel painful on the damaged part of your colon. When I have a flare up, I drink fruit smoothies a lot (not like ice cream, actual fruit or veggies). this keeps you full, but no hard particles are going into your system so it feels a lot less uncomfortable.
If you're feeling terribly constipated, you can use Colace or any other generic brand stool softener. The generic is 4 dollars for 100 pills at walmart (or any other similar store) and it will make it easier and a lot less painful to go.
Unfortunately, this will probably last until you can get in to see your GI doc. Hope you feel better soon.