Re: Blisters? Cold Sores? Any difference?
If it really is a "blister", it would sound suspiciously like herpes if it recurred in the oral area. However you may have some kind of mouth ulcer or canker sore. As the above poster says, if it's inside the mouth, it may well not be oral herpes although it still could be.
There are two types of herpes - type 1 and 2 (there are actually more kinds than this, but these are the relevant ones for this post!) The first, type 1 causes the vast majority of cases of oral herpes but can be passed onto the genitals via oral sex (or via genital sex with someone who has it in their genitals). Type 2 causes the majority of genital herpes outbreaks but can also in rare cases be found on the mouth.
If you do have herpes of the mouth, chances are it is type 1. This is very common (studies show 40-80% of the population have it, although most don't get outbreaks) and it does not indicate anything about your genital herpes status that you have mouth sores. Most oral herpes is passed onto kids by family members and friends etc and doesn't relate to sex. If you think about it: if someone kissed you in a purely platonic way, you could get oral herpes from them. No need to have sex there.
If you do have oral herpes, you should know that you don't have an STD. You do however have something which could be an STD in someone else (if you passed it onto their genitals via oral sex).
The best thing to do would be probably to go and show these "blisters" to a doctor, soon after they appear. A good doctor should be able to tell you what the problem is. You may want to ask them to swab the blister to test to see if it is herpes.