Thanks for posting your query at DoctorSpring.com
I can understand your concern.
This seems to be herpes simplex. Its caused by the hsv 1 or 2 virus. Its also known as cold sore and usually surfaces when there is a stress maybe physical or emotional which results in lowering of a person's immunity.
Taking prednisone could have been responsible for it since its an immunosuppressant.
I would recommend that you take tab. Valacyclovir for the same. Application of mupurocin cream on the lesions twice a day will aid in the healing.
Please let me know if you have any queries.