Check the tank's buffs in the party/target window to see if they are using their cooldowns, If you see nothing then you gotta start pulling healing potency from the book of magical wonders.

Expedient is definitely good to use when travelling to pull more dungeon mobs, it's definitely worthwile to use and provides some light mitigation while the tank is rounding mobs up. Though, if the tank is undergeared there is not much that can be done about that situation.