Do you have an actual diagnosis of IBS - or is it self diagnosed? I only ask because, if it's something with similar symptoms like Colitis... You need actual medicine. I tried peppermint when I was misdiagnosed... Made things worse. See your Doctor.
Peppermint hard candies are easy to carry, and help when I'm away from home. Also, a few fresh leaves sprinkled on my salad before meals, and tea with fresh mint are other ways I help myself. I've had ulcers for over about 20 years, and peppermint has always help me.
I find a chamomile and lavender tea works well for IBS because of the calming effect it has on both the mind and body. Traditional medicinals makes an excellent chamomile lavender tea but it may be hard to find. I am sure that the same brand makes a tea just for IBS. yogi tea may as well. Just look around and see what you can find. Best of luck
While I agree a doctor should be your go to place first and foremost if you wanna try some additional help with herbs then peppermint might help.
The problem with IBS is its an umbrella term and a lot can cause it, I myself have it mildly and they have no idea why (likely hereditary). Another option might be ginger, as ginger root has been known to sooth upset stomachs. Another option, while not herbal, is simply drinking warm water. Like a hot shower on your body, warm water can reduce cramping. And yet another option is Bananas! The pottassium in bananas is used for muscle control, it might help too.
Overall a doctor and chemical medicine, unless you visit a REAL certified herbalist, and your best first steps. Herbal magic and my suggestions should only be present to assist. not to be at the forefront.