Welcome to the IBS forum!
I am inclined to think you don't have IBS. There are the Rome Criteria
for diagnosing IBS. One of the main symptoms for diagnosing IBS is change in bowel habits for at least 12 weeks. To me it sounds like your bowel change may be caused by stress. Maybe even your diet. Do you have any pain or bloating as well?
Either way, if you are worried even in the slightest, you should see your doctor. Here is a brief list of IBS symptoms:
ROME II SYMPTOM CRITERIA FOR IBS
At least 12 weeks or more, which need not be consecutive, in the preceding 12 months of abdominal discomfort or pain that has two out of three features:
1) Relieved with defecation; and/or
2) Onset associated with a change in frequency of stool; and/or
3) Onset associated with a change in form (appearance) of stool.
Other symptoms that are not essential but support the diagnosis of IBS:
- Abnormal stool frequency (greater than 3 bowel movements/day or less than 3 bowel movements/week);
- Abnormal stool form (lumpy/hard or loose/watery stool);
- Abnormal stool passage (straining, urgency, or feeling of incomplete evacuation);
- Passage of mucus;
- Bloating or feeling of abdominal distension.