I used NFP for quite some time. Works well, but there will be many days you will need to avoid sex "just in case" if your cycles are irregular. We found it to be sort of a pain. As for the irregular cycles, just keep some tampons in your bag at all times and live with it. Also start paying attention to signs of your fertility, as this can help both with avoiding and also with when to expect your period (usually 14 days after you ovulate). I suggest picking up a copy of Taking Charge of Your Fertility by Toni Wechsler. Great book.