Your toughness is very low. You're currently around T10-T13 range. You need more than 9 mil toughness to survive. Around 25 mil toughness is average for most players pushing 80+. Monsters do more damage as you go up higher in tier. Therefore you need more life to sustain the damage and avoid getting one shot killed.
When you get more Ancients, you'll have more vitality. You have 9 pieces of gear that are non-Ancients which is roughly around 1000-1800 vitality that you have yet to obtain depending on how you optimize the gear when you do get it.