Seems it to be like an oral wart or a canker sore due to viral infection. I recommend you to eat garlic and it should disappear in a week.  But the first thing you do is to report to your dentist as any unusual growth should be reported immediately without any delay. Never attempt to remove a wart yourself by burning, cutting or any self developed method. 

For more info on such topic visit the link...http://www.identalhub.com/article_various-stages-of-cold-sore-blister--315.aspx