How do you figure out where you are in the cycle?
133. The four-week cycle of the psalter is coordinated with the liturgical year in such a way that on the First Sunday of Advent, the First Sunday in Ordinary Time, the First Sunday of Lent, and Easter Sunday the cycle is always begun again with Week I (others being omitted when necessary).
After Pentecost, when the psalter cycle follows the series of weeks in Ordinary Time, it begins with the week indicated in the Proper of Seasons at the beginning of the appropriate week in Ordinary Time.
Find out what week in ordinary time it is. Divide that number by four. The remainder is the week of your cycle. If the remainder is 0, the week is 4.