It could be a clogged pore with some dry skin around it- it doesn't sound like a cold sore or anything of that nature. Sometimes clogged pores can take some time to heal, they seem like they are better and can come back. I would just keep it clean, use the Vaseline if it helped, and if it continues to bother you- see a doctor to have them take a look. The doctor will be able to give you the most accurate diagnosis since they can take a look in person and gather more of your medical history.