Pardon me for sounding a bit short but for Heaven's sake, your license is your income, it is your livelihood. How could you wait until you are "coming up" on a renewal before taking time to understand what that license means and what you have to do to keep it current?
Call me an old grump but I really think the academies need to spend a bit more time teaching snowflake that continuing education is part of a professional career. License management is probably more important to a mariner these days than the latest stack of STCW "management" requirements when it comes to earning a living.
If worst comes to worst, if no one comes out of the woodwork to take you by the hand (and if you have a CG license) take the huge step of Googling "USCG license renewal" and do some reading. If that is too difficult, Google "license consultant" and pay someone else to read your future for you.