Im not a stam nb but a few things stand out to me from my pvp experiences going up against them so here are my suggestions for what they are worth.

You are going dw on your main bar. That's fine. Consider 2h on your second bar for rally. Or you can go bow and get the dodge roll speed bonus when you are evading/escaping

Primary attack bar. Ditch swallow soul. Flying blade instead. The heal won't help you at all speced into stam and rally would be a life saver for you on the second bar. You are probably using quick cloak as a gap closer to get the stun on surprise attack. Replace rending strikes with dark cloak and you can improve the combo greatly and once your stealth is blown in combat you can still use the combo. You will have to manage your magicka though in combat but if it is your primary magicka dump it is doable.

If you gear up right with something as simple as hundings and some cheap way of the air you can get a decent build. If you have the cash you should get some tong daggers and jewelrr/armor for the dw.

Go to the tamariel foundry forums for nb. Lot's of builds there to look at.

Edit: flying blade instead of dagger. hadn't used it in a while.

Pick up siphoning strikes-> siphoning attacks and replace swallow soul with it. You'll do less damage per attack but you'll almost never run out of stam, especially if you are animation canceling light attacks in your surprise attack spam.

For healing, pick up a 2 hander and level it up to rally, switch to it every 30 sec to refresh the buff (it also increases weapon damage to negate some of the siphoning attack loss) and go back to your dw if that is what you like to dps in. Bonus healing if you change rending to bloodcraze on your main bar as you can keep 2 HoT's on yourself during boss fights (though it is not the best for damage)

Surprise attack should be your main damage source as it keeps shadow barrier up, breaks armor, and does solid damage.

As was said before, check out Tamriel Foundry for builds, there are many and the people are generally willing to help talk you through a build.

I've been playing a stamina NB recently. I use a combo of Reaper's Mark to soften them up then drop Lethal Arrows on them until they close. Then I switch to Dual Wield and go Ambush/Heavy Attack until they're dead. It works pretty well for anything but bosses. For them I've got Veil of Blades. There are very few monsters, even bosses, that won't fall to that combo.

I wear full medium armor with all the perks for stamina. I run about even on health/stamina in attributes and chow down on blue health/stamina food. That seems to work well for me.