Re: 9 month with blister in mouth????
I think that if it's been there for more than a few days, you might want to call the pediatrician's office and just mention it to them, and see what they say. It could be related to mucus/saliva dripping down his throat from his runny nose and the teething. Chances are that it's nothing really to worry about, but in the event that it's something more than that they're aware of it. This way, if they don't think it warrants a sick visit, they're at least aware of it for when you do go, in case it's still an issue at that time.
Hope he's better soon.