you say you've had lots of tests - have you had a colonoscopy? That's pretty important. ALso, have you been seeing a GI?
Read all the diet guidelines and get started! If you love to cook and eat, I'd really recommend "Eating For IBS". It's full of fantastic recipes off really yummy food. My DH loves food too and he loves Heather's recipes. We hardly miss anything we used to eat.
Stress definitely makes IBS worse. You might want to consider taking up yoga or doing the hypno program - both approaches have really good track records.
I'm not sure what that drug is. As you're D, I'd (personally) recommend taking Immodium every day as a preventative and getting some enteric peppermint capsules which are a very good anti-spasmodic.