Blisters in back of throat

Last wednesday my boyfriend was doing some heavy work outside when he got caught by the rain. The next day he says he drank an energy drink, which got him all energized. Suddenly he got really weak and he had a sour taste in his mouth and his throat was hurting. He noticed he had some sores/blisters in the back of his tongue/throat. He has been like that since, seems like they get worse. He now has 2 blisters on the outside of his neck and a couple on his back. He can't eat because its painful. He had a slight fever on sunday but it went away. He seems weak. What can this be?
He has been under alot of stress lately. Then he doesn't know if the fact that he was caught in the cold rain had anything to do with it.
Can anyone help? I will be taking him to the Dr tomorrow though. Tweet