You should definitely see your doctor before you try taking anything for the problem. IBS is an issue that can be caused by underlying problems, stress, allergies, etc. Talking to your doctor can give you an answer as to why you have the stomach issues. While there you can ask if they think peppermint tea would help or make it worse, often IBS is triggered by certain types of food and peppermint may make it worse rather than better.
The doctor can prescribe you with something that helps with the problem, and once diagnosed you can actually buy herbal remedies over the counter for the issue, but it is not advised to take any herb unless you know it will not make the problem worse, give you side effects, interfere with medication or give you an allergic reaction.