As level 43 you're more than likely missing a lot of key skills that a Magicka NB needs to deal decent damage. Such as Proxy, Mages Guild 10 (for Might of the Guild passive), Inner Light, etc.

Here is a quick rundown of what you could run. Keep in mind I am dumbing down some of the skills and gear due to the fact of your lower level.

5x Kags or Julianos (prefer Julianos for 1vX)
4x Magnus (3x with staff)
3x Warlock Jewelry (for low level like yourself)

Use Tristat food or Stam/Mag regen drinks. Thief Mundus for moar crits. Can use Atro Mundus if you feel Magicka regen is an issue, but with Siphoning Attacks always up this shouldn't be a problem.

Use Destro/Resto or DW/Resto

Bars (DPS);
Funnel Health
Merciless Resolve (or fear)
Cripple
Entropy (or Concealed weapon)
Dark Cloak
Ulti: Batswarm or Soul Tether

Bars (Back);
Healing Ward (or Blessing of Protection, your choice)
Impale
Sap Essence
Proxy Det (or utility slot being you probably do not have proxy yet)
Siphoning Attacks
Ulti: Soul Harvest (single target ultimate, also regents ultimate for enemies killed)

Can remove Entropy and Impale for Inner Light for more crit and max magicka.

End all be all is that Magicka NB is in a poor place for 1v1 or 1vX. The damage just isn't there, especially at lower levels. You have to rely on your ultimate and proxy det for burst. IMO, Magicka NBs are the least feared opponents on the field. They're more like that pesky fly buzzing around your face.

If you consider doing stamina I highly suggest you do it because it's better on a khajiit