Okay, so: yes, Brie can smell pretty strongly of ammonia, and it doesn't always mean the cheese is bad.

Brie is a mold-ripened cheese. The mold that forms its white rind feeds on the proteins in the cheese as it ripens, and one of the things it gives off is ammonia. In a shop's cheese case the cheese can breathe, so you never notice. Wrapped tightly in plastic, or kept very cold, the ammonia has nowhere to go and builds up.

What to do about it:

1. Unwrap it and rewrap in wax paper or parchment, then put that in a loose container or unsealed bag so some air can get in.
2. Before serving, leave it out for at least 30 minutes. The smell fades as the cheese comes up to room temperature.
3. If there's no visible mold growth, it's probably fine to eat. If it still tastes too sharp for you, it's past its best, and you can bake it or just let it go.

Related: What is the difference between Brie and Camembert? · What is the outer layer of brie cheese? · Can you bake Brie or Camembert? · Can I eat the rind of cheese?