It is fairly common for women to experience some irregular bleeding while on the contraceptive pill, especially over the first few cycles of use or when a pill is missed. Uterine bleeding can make a woman niddah even when unexpected, as during the active-pill cycle.
Whether or not you are currently in niddah depends on the nature of the bleeding you have been experiencing. If you experienced a blood flow, or saw blood exit your body, you are in niddah. That seems to match your description. In that case, you could consult your physician about stopping your active pill cycle early, so that you need not spend a prolonged time period in niddah.
If you have had heavy staining, but not a full-fledged flow of blood, then your status depends on the color and size of your staining and the surfaces on which it's been found. For more information, please see our article on stains. Then please write back with any follow up questions.