Why does no one really take my disease seriously?

Especially in a uni or work context I feel like people don’t get what it means having a flare up. Maybe I’m just really bad at coping with my flare up but having extremely painful cramps and having to go to the bathroom 15 times a day makes me just way to tired and exhausted to do anything for university. And when I tell the professors that I can’t come to their lectures because I’m in pain and am sitting over the toilet the whole day they just give me stuff on top to do to make up for me missing the lecture. It’s like what don’t you understand about me being in pain and basically not able to move. Now I have to force myself to go to uni because if I don’t they will give me even more stuff to do, which puts even more stress on me and feels like it’s getting even worse. Sorry for the rant. Maybe I’m just overreacting.