If enemies in a certain area, such as Hell, are too tough restart the game. Enemies such as Flesh Spawners, Stygian Hags, and the Hell beetles can spawn dozens of creatures in seconds. After restarting (exit, save, load, and play), check the area and repeat if needed. The Hell beetles are usually replaced by Doom Knights and Venom Lords, and the Hags are usually replaced by the same. This may also work with other areas.