If you seriously think you may have an allergic reaction or toxic megacolon, you should get to a doctor or hospital asap. I don't think anyone can say whether you're dealing with normal UC pain or something worse from your descript
ion. I don't have physical pain in my stomach but I do have cramps when I have to use the bathroom and a lot of urgency. When I was in a really bad flare I would use the bathroom 15 or 20 times a day, every time losing some blood. I would also have a lot of bloating and gas.