Some people don't react well to Asacol. Interestingly enough, it can actually increase symptoms in some people. Side effects listed on WebMD:
Headache, vomiting, nausea, dizziness, weakness, upset stomach, diarrhea, or gas may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
It's worthwhile to try a different ASA. I was switched from Asacol to the older drug, Azulfadine (Sulfasalazine), and have done really well on it. Keep in mind when you're really ill, it can take a while for the colon to heal, no matter what route you go. It took me over two years of trial and error with meds, diet, probiotics and other supplements to figure out what worked for me.
Regarding your diagnosis, after years of thinking I had UC, my diagnosis was in question recently. After some expensive blood tests, it was decided I probably DO have UC, yet I have "thickening of the bowel wall" on the right side, which is not typical of UC. So, cases are not always clear cut.
Diagnosed with ulcerative colitis spring 1999
Therapeutic dose sulfasalazine.
Probiotics, l-glutamine and fish oil caps. George's aloe vera juice and Mucosaheal.