What are the expiations (kaffarat) incumbent upon me after repeatedly breaking my oath not to speak to a young man? Am I required to fast for a full month? And can I postpone the fasting until after Ramadan?

You are liable for an expiatory offering (kaffarat yamin (definition)) for the second oath due to breaking it. As for the third oath (yamin al-lajaj - an oath uttered in a fit of anger or stubbornness), you have the choice between fulfilling what you swore to or offering an expiation for an oath. If you do not fast the month, then you owe two expiations. If you do fast it, then you owe one expiation. Fasting the month can be done either consecutively or intermittently. The expiation for an oath is feeding ten poor persons, or clothing them, or freeing a slave. If you are unable to do any of these, then it is fasting for three days.