There is more than one type of anti-spasmodic out on the market; tell your doctor that yours isn't working and you need to try another kind. The kind I got put on has never helped me any either. A lot of people have to tinker with anti-spasmodics to find the one that works for them.
Also, have you tried a different brand of fiber? Some people don't seem to react well to certain brands. I know the FiberChoice pills made my constipation worse and my diarrhea worse (can't win for losing!) and I seem to recall that some people who are fiber-adherents have said that one brand works better for them or gives them less gas than another brand; you just have to experiment with that too.
And have you tried the calcium for your diarrhea? Depending on what's causing your pain, it may not help with that any, but it did help mine and fixed my diarrhea. And have you tried anti-gas pills to see if that helps the pain? You may have trapped gas down there; I think gas can pretty much lurk anywhere. And then there's always the probiotic route. Ask for a test for bacterial overgrowth. There's supposed to be one out where you just breathe into a machine and it analyzes whether you have too much bad bactiera in your guts. You can also get migrating bacteria which sets up shop in parts of your colon where it's not supposed to be; I think that will show up on the test as a bacterial overgrowth (since you have it in extra places). They can fix that with antibiotics and probiotics, but you can always try some probiotics even without that diagnosis; they're good for everyone. May cause a little gas at first, but you should adjust to it. And some people do get relief, in the end, from their gas, bloating and even from their diarrhea or constipation. If bad bacteria is your problem or part of it, the probiotics will help to some degree, at least.
When I went to the doctor complaining of a bad gall bladder, they tested my gall bladder, then did an endoscopy and colonoscopy and that was it. Everything came back either clear or inconclusive (the hida scan--a second one came back clear), so I got labeled as having IBS (I really did have a bad gall bladder, though). Some doctors will only do a colonoscopy; if you don't have UC or Crohn's, they'll pronounce you to have IBS right then and there. Some, though, will do CT scans and small bowel follow-throughs and camera pills. It's up to you to decide if you want all of those tests or if you are comfortable with accepting the IBS label. But I think you should ask about the bacteria overgrowth tests and have some stool samples checked for parasites and things like that, especially if you travel outside of the country or deal with animals daily or walk barefoot a lot or have drunk from a natural water source: those are all ways to catch a parasite. If you live in a big city and haven't traveled anywhere lately, then you probably don't need to bother with it.