I'm really sensitive to insect bites and when I get bit by an insect, I almost always get a small cluster of blisters in that area. My doctor says it's a minor allergic reaction from the bite.
The only way I can heal the blisters is by using a topical cream for allergies. Ones with corticosteroid in it work really well. The blisters usually go away in a day. Otherwise they stay around for longer.
Thankfully, the blisters aren't painful. They're just red and itchy and even though I want to itch them so bad, I resist. Because if they pop, then they start to hurt.