Plz answer! Blisters?!

For years now I've been getting random blisters/sores on my tongue and only my tongue not on my gums or mouth....

And idk why... i do not have herpes ive been checked for everything... so why do I keep getting these ? Anyone know what these could be? Something serious? I am currently 4 months pregnant..

Its usually only 1 sore/blister on the side on my tounge, or the tip of my tongue sometimes the base of my tounge. I've looked on Google and no answers... help plz