This is more common than you may think. It could be stress related, or it could be a food sensitivity of some kind, or even a combination of both. If you can think back that far (which can prove difficult for anyone who's missing sleep or experiencing stress, like we mammas so often are) consider whether you've added anything new to your diet, or if you've increased the amt of some food or drink (cappuccino anyone?) you ate less of before.
If this proves difficult, you can keep a small notebook on hand, and just jot down what you eat through the day, and see if you can discern any pattern there, btwn foods you've eaten and flair ups of the condition.
And lastly, consider talking to your family doctor or general practitioner to ask about Irritable Bowel Syndrome. It's worth asking, and the doctor won't even flinch, I promise. (I have it myself) He or she will be able to direct you to a specialist, or tell you which tests you may need. Best of luck, I know this can make life a bit more difficult, and I'm sure you don't need it right now. Feel better soon!