I suffer from IBS, depression, and anxiety. I didn't start taking an antidepressant until about four or five years after I was diagnosed with IBS. Taking the antidepressant has helped me tremendously in terms of my IBS. It truly can be a vicious cycle, but having your anxiety under control can really help with the IBS.
The antidepressant isn't the only thing I rely on to help with my IBS, though. I have tried to educate myself as much as possible about IBS and try to avoid trigger foods. I also take Citrucel everyday which also helps so much. Like you, I have IBS-D and didn't think fiber would help. But it really does. Taking a peppermint pill before each meal also helps me. The helpforibs site has a wealth of helpful information for IBS sufferers.
Don't let IBS or any other health condition control your life. Try to get it under control so you can live as "normal" a life as possible.