Just like any other muscle, your abdominal muscles may feel sore or stiff a day or two after you try a new -- or newly challenging workout. If you're feeling stomach pain that's not in your muscles, though, it might not have anything to do with your abs. In that case, you should seek advice from a medical professional.
Don't Overdo It
Although some muscle soreness is typical after any challenging workout, if the soreness lingers for a few days you probably overdid your last workout. Next time, ease off your workout a bit by doing either fewer sets and reps or an easier version of the exercise.
Other Possible Causes
If you feel any sort of sharp pain while exercising or any stomach discomfort that's not from the muscles you're working, you should speak to a doctor about your symptoms. Other possible causes of stomach pain include infections, viruses, a variety of bowel syndromes and appendicitis -- nothing you'd want to mess around with on your own.