If you're going low carb, ditch the potato and bread products. Those will thwart your progress big time on that way of eating. You'll likely see more success following a specific plan than general low carb (Atkins, nutritional Ketosis, South Beach, Stillman's, Dr. Bernstein, Eat Fat Lose Fat, etc).
As for your stomach acting up, without hearing more details on your menu and health history, it's really hard to say. Could be a stomach bug, food intolerance, gall bladder issue, you name it.
That said, I've noticed my own low carb eating does indeed get things moving. Lots of fat and plenty of fiber equals frequent and easy bathroom visits. If I eat too much coconut oil, that becomes a little more urgent