I Have Had Ibs For More That 20 Years. About

I have had ibs for more that 20 years. About 8 weeks ago I changed my diet to a plant based diet. For 4 weeks I had no symptoms. Now I have diarrhea and several times a day and cramping so bad that I have started vomiting, almost daily. Sometimes I skip a day of vomiting. I can't eat anything after 5 pm or I will be up at 3 am to 5 am with diarrhea. With the diarrhea I cramp so hard I gag and heave even if only bile comes up. I have lower back pain and it sometimes feels like the pain shoots from my back to my intestines