Hello and welcome! We are glad to have you here.
If you have had full exams by your gynecologist and everything is in the clear, then you are probably just having common irregular periods. Unfortunately, a lot of women go through this at some time in their lives. It may stay for a very long time, it can come and go, or it might become regular and never act up again. There is just no way of knowing.
However, if it's a really big inconvenience or annoyance for you, many women take birth control to help regulate their periods. I don't like to recommend birth control unless it's really necessary, but I wanted you to know that it's an option. It may take some trial and error finding a birth control that is just right for you so keep that in mind.
If your period become more unstable, I would just be sure to get regular check ups to be on the safe side.