My initial guess is that if there's a small white head with a puffy appearance, its a fistula from a dental infection. I would recommend seeing your dentist to verify the source of the infection and getting it treated soon.
I think its both. First go to dentist and then to sinuses.
Aphthous ulcers usually begin with a tingling or burning sensation at the site of the future aphthous ulcer. In a few days, they often progress to form a red spot or bump, followed by an open ulcer. The aphthous ulcer appears as a white or yellow oval with an inflamed red border.