It depends on whether the pregnancy was molar or not. If you lost a molar pregnancy, then you DO have to wait a year because there is a relationship to cancer risk if you do not. But if you simply had a miscarriage (I know, there is nothing simple about a miscarriage, but I mean if the pregnancy was not molar) you can try again after two normal periods.
You can try again after your next cycle, but if you wait longer it may decrease your chances of miscarrying again.