Herpes simplex (cold sores) viral infection can be triggered by trauma, and this is a. Ery common area for such cold sores to occur. Perhaps the trauma of the filler injections triggered a recurrence.
You may want to take Valtrex before your next treatment to prevent such a recurrence.
Is possible although unlikely that this could be Juvederm Ultra hyaluronic acid. This product is meant for shallow subcutaneous treatment of fine lines and wrinkles. With this use I would say it is extremely unlikely to develop the problems that you have. Injection that was excessively deep in an effort to restore volume might cause a gel-like drainage. You should return to your injector.