http://www.medicinenet.com/miscarriage/page3.htm
Unscheduled and irregular bleeding is an indication of something not normal going on in your body and you should have seen a doctor already. Check the link above and learn that there are many different symptoms and causes,of which miscarriage is just one. If you have been sexually active without protection then that is a likely 'diagnosis', but as I said there are many reasons for this and should not be taken lightly. So, please make an appointment, or go to the ER as soon as possible.
Ignoring or under-rating your body's signals is something we women should never do.
Get reassurance from your physician, and good luck. Please keep us posted.
http://smileys.smileycentral.com/cat/16/16_4_7.gifGet well soon!