What is this?

Looks like a cluster of about 4 white blisters under the skin. Nothing at the surface. Popped up yesterday out of nowhere near the crease of my thumb. It is very painful. There is nothing stuck under my skin that I'm aware of.

-I have had a sinus infection for about a week.

-I do have herpes.

-I am 21 weeks pregnant.

(Just a few ideas of what might be causing it).