One thing that might help you decipher what it is - when it occurs, use a flash light and have some one take a picture every day. Keep a log of when it occured (dates), how long it lasted, pics of it, what did you eat for the last 2-3 days before it come up, and what mood were you in (extremely stressed/angry, etc)

I will get canker sores in my mouth and on my tongue if I eat too much Vit C - acidic foods. Also potatoe chips will tear up the roof of my mouth and gums.

But white blisters that pop.... I think I would wait till that comes up again and would go to the doctor. The only time I've had that is when I caught a virus.

And yea, you can have herpes for years and not know it. Depending on the strain and the stegnth of the virus - you may never see a break out unless under extreme stress (mental or physical).