Well the difference between 19 days and 21 days is ... a whopping 48 hours!
You have a very short menstrual cycle at present but this can go up and down and back up again over the course of time.
If you are particularly concerned you can discuss the matter with your GP who can do some baseline investigations and take it from there.
I went through a transient phase of having periods every 14 to 15 days after a spell of over 4 months with no periods at all, after which everything normalised without any intervention and I went on to have the perfect textbook 28-day cycle thereafter.