So I got my monk to level 47 and I have about 14,000 HP. I'm stuck on the part where you have destroy the catapults, there is just so many mobs I get overwhelmed every time. I've also been switching out skills/runes and only seeing a marginal difference and still dieing.
Try joining a group, or getting a higher level.
Also, move out of the way from the attacks of the guys that dig in to the ground and plague the area where their fist comes out, they do a ton of damage and if multiple do that to you at the same time it's game over.
Use wave of light for spacing and heals with transcendence.(spam this spell)
Use Inner sanctuary for defense and breathing room.
Use breath of heaven for heals/ dmg boost
Serenity is your Panic button.
Snipe with Deadly reach and Throw down Inner Sanctuary to keep them off you while spamming wave of light.
This is my build for group play and I am currently lvl 56 (hell act 2) and can survive a ton of punishment. With some situational awareness you can survive any encounter.