Pretty new to Planescape and all Baldurs Gate/Icewind/Fallout style classic RPGs so forgive the pretty stupid question.

I'm not too far into the game but I am finding that I am just dying really frequently... to the point where its really interrupting the flow of the game for me. I know that dying is not such an issue in this game and in parts is used for puzzle-solving etc but I am talking about combat deaths...

I lose hit points so quickly that in most battles I have to run off and let Morte do all the fighting. If there are any more than 4 enemies, my character doesn't seem to stand a chance! I have upgraded my CON skill to 14 so it's not that low.... I don't get it.

Am I missing something?

What are you fighting? You may just be getting into fights you're not supposed to, or with enemies too strong for you.

Also, did you recruit additional party members? You can probably finish using just Morte and TNO, but fights are really balanced for more people in your party.

As for characteristics, the ones that enable you to be a better tank are dexterity for AC and constitution for hp. Both only give bonuses if they're above 14. You can pretty much ignore dex in this game (unless you want to play as a thief) since there is no armor available and you'll get hit almost every time anyway.
Con only gives you more hp and higher regeneration.

In other words, it's normal to get hit all the time if you're using TNO as a tank. You should be concentrating on killing enemies as fast as possible, and you should be recruiting Dak'kon ASAP (he's in the bar with the burning man).

It could be that you lack skill with the weapon you are using; with fists and edged weapons, TNO starts out with pathetic skill, which results in him doing less damage and hitting less often; same goes for the other weapon types, but since TNO's skill in those is even more lacking, the problem becomes even more apparent. Check your character sheet and see how many plus marks you have next to each weapon type; if it's one or less, you need to get someone in the game to train you.

Thank you all.

I am starting to make a bit of progress now and have 4 characters in my party so fights are more under control!

Will report back if anything else completely stumps me!

Con is the only combat stat you need. Raise it if you have trouble.
It helps using the spells and skills your companions have available, not only Morte can increase his damage output a lot if you cast a strength spell at him for example.