I often tell women that one missed or "weird" period per year is nothing to worry about.
The series of events that produce a "normal" period are complex and involve many components. Remember that our calendar is based on a "solar" system, whereas the true meaning of month is related to the moon. There are slightly more than 12 lunar cycles in a calendar year, so your period won't fall on exaetly the same day of the month, every month, unless you are artificially regulating with a birth control pill. The average length of a menstrual cycle (from the first day of bleeding to the next month's first day) is 29 days. However, anything from 23 to 45 days can be normal.
A woman usually needs at least 20% body fat to menstruate regularly. Low body fat is one reason female athletes do not have regular periods. Stress, travel and a change in sex life are other factors that can change the rhythm of your period.
Regarding the progesterone you were given: When you stopit, you should get your period within 1.° days. If a "progesterone push" indeed produces a period, then your gynecological system is working and your period should normalize on its own. If the progesterone does not produce a period within 10 days, then further testing is required.