Hi Eronaile,
i had the same problem , being stuck at loosing every major fights at lvl 4 . as the others suggested , i went to a big city and runned side quests to reach lvl 5 , big difference.
i also started to kite enemies. the ogre queen i did kit her untill her minions left and only her was remaining on the battlefield. to achieve this i had to bring her on the other side of the bridge. in oder to kite i use the rogue or the ranger's pet. of course your ranged characters can shoot the foe during the process
and you can set traps in advance on the path you plan to kite the foe
consider kiting as a true combat phase, with slow time and pause abuse... send the rogue scouting , agrro one or two foes at once, kite them to your group, kill them, repeat.
you will see some monsters going back at some point , shoot them for re-agrro.
the other key point is the crowd control. wizard spell Slicken is a must have.
edit : i play on normal , started infinite paths lvl 4 , now 5, figthter ( tank ) priest (me ) , priest ( durance ), wizard , rogue, ranger . i've reached infinite path 6th floor without major problems, some sweating time to time ^^