Thank you for writing!
You were put on the birth control pill to try to regulate your cycle. Most women with PCOS have irregular cycle with very light periods or no periods at all. This makes pregnancy difficult. It's good that you did get a period, even a light one. Periods while on the Pill are generally light for all women but the fact that it is light isn't something to worry about.
There is no cure as yet for PCOS but the birth control pill can help with symptoms.