I'm sorry you're having attacks! But just remember that even though this medication helps, it's not a cure, so you are still going to have attacks now and then. That's the problem with IBS - sometimes you will have a random attack which isn't always related to food (it could be hormones or stress or ???). I would say to keep on taking it for 6 months to a year and then see how many attacks you have during that time. I know that when I had an attack, I'd panic and was unable to "see" that overall I was actually doing better. I'd say that after a year you should be able to see if it's really helping you by decreasing the number of attacks.
If you want to increase the dose, ask your doctor if you can take an increased dose every other day or just go up by 5 mg. In the meantime, keep following Heather's diet and advice and taking your medication. Maybe you could BTC for a couple of days. I hope you feel better soon!