If you already have 15 health potions or 10 other potions in your inventory, the game is less likely to give you more potions as random loot drops. You can fool the game into thinking you have less potions by going home and dropping some potions into storage. After that, loot a dungeon and the game will give you more potions in loot until you reach the "cap." Repeat until you have the desired number of potions. Eventually you'll be rolling in health, lyrium, and stamina potions. If you don't need them, sell them for coin.