Mouth blisters?

So I’m a first time mom, my son is 15 months, I noticed he’s been fussy these past 2 days when he eats so I looked in his mouth and I saw blisters on his tongue. They’re red, some white, and I’m very worried. It’s late at night right now and I’m tempted to take him into the ER. Are mouth blisters common at this age?