How can I increase my health?

I'm a level 16 warrior/monk and I have 400 hp. It seems like I should have way more, especially since a 15 necro/monk in my group told me he had 350. Is there a way to increase health other than runes?

Everyone has the same base HP at the same level. The only things that change(i.e. increase) that are Vigor runes, and equipment that grants HP bonuses under certain conditions, like being enchanted (some shields have HP+ with no conditions).

You can also use skills like Endure Pain to increase your HP.

Thanks

There are also non-conditional HP bonuses available from weapon mods. The +armor mods are frequently better at keeping you alive, though.