While your bronze count may reset, it's only because that 100 bronze was converted into 1 silver. 100 silver, when you reach, it, will be converted to one gold, and the remaining silver you have will be displayed. Gold then goes up to around 100k, I believe, then it caps.
So your counter would be something like: GG SS BB. G is gold, S is silver, B is Bronze. You aren't losing any money, don't worry!
Medals are PvP rewards that can be used to trade in for items in a medal vending machine. As of now there are only silver and gold medals. You accquire them from dungeons or turning in PvP dog tags.