What Is Functional Bowel Disease ?

Question: I have a problem every few weeks of yellow drainage from my anus. Sometimes it has no smell and other times it is 10x stronger than body odor. After this happens I will have a horrible burn like fire and it feels like i am sitting on a broom stick. I am aware immod causes a little tightening etc. I am aware of fissures and do get them sometimes. But there seems to be massive swelling that puts pressure on my prostate and makes it feel like I need to urinate during a 2 day attack. There has been a dullish red color blood lately, I feel buldging and extreme pain even with a 1/2 inch stool or teaspoon of diarrhea. The problem is concentrated to the first two inches inside my anus. I will have small flaky pieces of light colored yellow stool. I have tested this with litmus strips and its 7 or 6. Nothing shows on sigmoidoscopy though. I have been seeing a specialist GI and seen an anorectal surgeon in case it was an XXXXXXX hem. They say IBS but I was taking six immod per day and 4 belladonna and it would still happen. So it seems it may not be muscle movement but bile or acid or bacteria prob. Which of these is the most common? Would it be that this is the beginning stages of chrohns or UC? I Had a upper endoscopy, small bowel follow through, celiac screen, abdominal ultrasound, gallbladder test with kinevac all ok, I have tried XXXXXXX active and organic greek yogurt and florastor and sustenex, and align at different times. I am taking prilosec in the morning and ranitidine at night per specialist. Sometimes these probiotics seem to help and other times they seem to cause pain around the belly button like SIBO? 33 male 5'-8" 225lbs.