What Causes Irregular Periods?

hello doctor,i'm having irregular periods.there is 15 days to 1month lag between 2 adjacent periods .i'm 23 years old.i had a tubal pregnancy 6 months back and my left tube is removed.my ht is 160cm &weight 65 kg.can i be pregnant again doctor.now my physician prescribed meprate for treating irregular periods.is it a good drug for this.