"I have been told my an MD that there Can be Only One big worm, but I think that is more hooey that doctors hand out to patients that they consider hypocondriacs."
There may be some truth to this. If you have worms that lay eggs, the female will emit a hormone that prevents her eggs from hatching until she dies. This is to prevent her babies from competing for food. The eggs won't hatch out if there are anti-parasiticals in your system either. That is why it is important to periodically take a break and give your body a rest. It is even more important to follow up with another round, to get the babies, otherwise you could get sicker than you were before you started exterminating, when the new hatchlings start mating.