How To Induce The Periods If Being Missed For A Long Time?

i had missed my menstrual period for about 3 months now i so some spot blood on 31st Dec 2010 and up to now my period is not normal is like some time you can see little blood one day the is about 6 days now since i sow some blood spot but this is not normal period at all kindly help me what tablet to take in order to induce my menstrual period to became normal and regular