Bit of a skill issue lol, fire enemies are resistant to fire, so of course a fire mage would struggle against them. Especially against these annoying lizards. A good tip is to think about what issues you'll have facing a side dungeon, and find a way to solve it or just avoid the dungeon, its optional. Usually I find a melee weapon or a different type of elemental spell if need be. Of course the game has balancing issues tho, this is like the early early release of the new installment. It's a frustrating game at times but with time you learn and get better lol