Ok, so my ibs and your is pretty different with a couple similarities. One difference is my IBS started after a freak stomach flu last year that lasted a week but the nausea and pain never went away so i had to take 3 MONTHS off work....ever since then my BM were never the same again! TOTALLY wacky and off kilter. cramping, bloating, hurt, pain, diarreah and mostly NAUSEA before and after BM's EVERY TIME leaving me tired, shakey, wiped out and gross till this day i still have it. Did a colonoscopy&Endo....came back normal! did test of celiac, chrones blah blah blah nothing! anyway I have always struggled with depression and anxiety and something told me that whatever was happening to my body (and truly this was physical!) that my mind was sending my stomach the wrong signals....so igot so much anxiety from feeling sick all the time i was admitted into out patient therapy after that I saw a psych doctor and I researched it and asked him if I could go on anti-depressants. NOT my number one answer but I had come to the point of desperation and and all the issues just didnt seem to add up so i had to be my own doctor. anyway I ended up going on an extremely low dose of prozac and an old medication called doxepin (dox is a med used for obsessive compulsive, add, and mostly IBS) also the doctor prescribed it to me cause i was so nauseated all the time and dropped 35 lbs! (was not that big to begin with!) and told me the meds would give me my appetite back. Well those meds together has helped ALOT! I am not cured thats for darn sure infact i struggle everyday and i am still trying to figure it out. still get nauseated before and after EVERY single BM for the last year which is when I initially had the stomach flu. SO strange, unexplanable, inconveniant, and very upsetting. and while i KNOW I could have it MUCH worse and am very thankful its very concerning to me. sorry I cant give you more help but I just want you to know there are other people who get it.
So I know yours is very different and THIS MAY NOT BE THE ANSWER FOR YOU but am merely giving you one avenue you might have not explored. I still hope to heal this naturally. trying to go see a hollistic doctor.