So I saw the Shot glass and said 'why not' proceeded to use it.
Well it says ' only two potions per combat' What it does tell you is that BOTH potions must be consumed on the SAME TURN, otherwise it counts both potions taken for the limit.

is this intended cause if so, this weakens the Relic Significantly, and I would not of taken it.
Simple fix (have it start with its limit # set to 2, and each potions taken lowers it by one, and that is the only condition to lower it. Once at 0, condition = cannot consume potions.
That should be a simple fix overall.