Welcome to HealthCentral's IBD site.
With regards to your question about Asacol and how it works - it sounds like you need to discuss your continuing symptoms with your doctor again. Are you seeing a gastroenterologist who specializes in IBD/UC? If not, it would be to your benefit to find one that does.
I'm not a doctor, I'm a UC patient, so the information I can give you is NOT medical advice, nor should you increase any medication doses WITHOUT talking to your own doctor. My first serious flare-up was 10 years ago and I was having 15-30 diarrhea BMs per day, was losing weight, etc. A colonoscopy confirmed a UC diagnosis and I was given a prescription for Asacol, 3 tabs, 3x/day (so 9 per day). None of the 5-ASA drugs, the family of drugs Asacol belongs to, are fast-acting, meaning they aren't going to settle down a flare in a matter of hours or days. They are drugs meant to reduce the inflammation in your colon and it can take weeks or months to really have an effect. It took me nearly a year or more to get my symptoms remotely under control with Asacol, major diet changes (you might want to read some of my older Shareposts here about diet, etc.), and major lifestyle and employment changes. I now take 6 Asacol/day as a maintenance dose which helps in keeping my symptoms under control. You may need to talk to your doctor about increasing the dosage until this flare calms down.
Or, it may simply be that the Asacol isn't going to work for you. It works well for some of us and not at all for others. You might need to try another IBD medication like Colazal. Again, talk to your doctor about the treatment options and also look into your diet - what I eat makes a huge difference to how I feel and my symptom level.