the chances of you getting pregnant on that are very very slim. I had horrible problems when the shot and 3yr iud thing came out when i got on them they couldnt get my periods under control. you need to go to your doctor and get them to check it because when mine messed up i bleed for a yr and a half before they couold get it back to normal
I don't know much about your birth control, but if it's not pregnancy you need to get to doc asap cause it could be some kind of health issue. If it is pregnancy the bc hormones aren't good.for the baby. Please go to the er or doc as soon as you can.