I missed two days of my birthcontrol, doubled up the two days like it said and now I've had my period for twenty-one days. What could be wrong?

Nothing. Most likely nothing is wrong. Today's pills are so low dose that when you miss pills, you may bleed for the rest of the cycle. Take a home pregnancy test, if neg, start the dummy pills in your pac, and then when thru with the dummy pills, start back on the new set of pills. Set an alarm for every day and remember not to miss the pills. If the preg test is positive, see your doctor.