There is no set frequency of the Holy Confession in the Orthodox Church, as far as I understand. It depends on local tradition. In Slavic cultures, you cannot receive the Eucharist if you do not go to confession immediately before the Divine Liturgy. On the other hand, in GOA this rule does not seem to be enforced. Actually, if you come to an Orthodox priest even daily and ask him to be the witness of your confession, the priest cannot refuse.
And yes, as a catechumen, I believe, you cannot partake in the Holy Mystery of Confession. I wanted to confess my sins when I was a catechumen (in winter 2007), but my priest said, wait until you are chrismated, because right now the confession will not have any sacramental value anyway. When you are chrismated, you are a member of the Body of Christ, and then you can (and should) partake in the Holy Mystery of Penance (or Confession).