Chronic Bloating And Constipation. Following IC Friendly Diet. Opinion?

I am a 36 years old female with more than ten years history of chronic bloating and chronic constipation . Different tests showed no abnormalities in my bowels, so Gastro suspected IBS-C and just recommended to manage with diet and laxative (Milk of Mg, Miralax, etc). I tried drugs like zelnorm and amitiza w/o success. Lactulose made bloating even worst. Also, off-label use of a drug similar to colchicine , which name I can t remember. This one seemed to work but stopped it because I was afraid of its teratogenic effects. High-fiber diet does not make a difference. Eighteen months ago, I gave birth, and bloating and constipation were a little better after delivery. About a month ago, constipation and bloating have been terrible again, and started to have symptoms like an UTI. The OB-GYN diagnosed me with Interstitial cystitis . I am currently, taking Elmiron, Hydroxyzine , IC-friendly diet, and having a series of bladder instillations. I feel better regarding my IC symptoms, but noticed that whenever the constipation and bloating are bad, IC flares up. Currently, I am having liquid bowel movements (with Milk of Mg) and noticed my breath and stool smell like a chemical substance. Bloating is still there, even if I have a bowel movement, and aggravates along the day. I am following the IC-friendly diet, but there are some things that are IC friendly (ie wheat), that aggravates my GI problem. I read about a low FODMAP diet, but I would like to consult a Gastro about these because I am feeling like doing both diets is very limiting. Also, I would like to have things under control as I am thinking of getting pregnant again. I am worry about nutrition, and gaining weight during pregnancy. I will see a gastro in a couple of weeks, and want to bring up this IC diagnosis, and possibly evaluate for SIBO or celiac. No Dr has ever mentioned any of these conditions, but I read that IBS-C and these have overlapping symptoms and you can end up being misdiagnosed. Can you please provide an opinion? I need some help in the meantime.