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Most probably this is Herpes Zoster or Shingles, especially if you have blisters over a whole dermatome, like forehead, scalp, and side of upper face.
You should take antiviral medication immediately so that deep scars and postherpetic neurlagia are prevented.
Read more on How to Manage Shingles
Uncommonly, herpes simplex blisters can occur on the forehead also, but this will be only a small group of blisters and not as painful or burning as in shingles.