Hello, I'm a level 18 DK at the moment and I found myself yesterday to be kinda weak. There was a boss that I had to fight yesterday and it killed me a few times and even when I managed to defeat it I pretty much struggled to do it. Also the irony is that whilst I was preparing to attack a sorc came, pew pew and killed it

).
I currently try to run something along those lines
https://youtu.be/tIUWhb_Uar0, though my 2H is just lvl 14 and I have neither the execute nor rally. At the 1h and shield bar I have Obsidian Shield, Volatile armor, Ransack, Unstable flame and fiery breath as a placeholder and for some extra damage. The thing is I never have enough magicka for Dragon Blood (this being on 2H bar in place of rally) when I need it because a lot the previous skills use magicka.
Should I stay stamina and level my 2H more or would it be better to respec my stats (I have 5 health and 12 stamina now) and go magicka with 1h and shield + destro staff and let the other weapons for later levels? I found a Laceration build on youtube which seemed interesting even though is from previous patches.
Oh also I know that the skill trees level up by gaining xp and having spells on cast bar, but do individual spells (like Dragon Blood for example) level at the same time or they gain xp when I use them?