So whats really bothering me in skyrim is that sometimes there are enemies who are much stronger than you are, in quests etc. I currently have the difficulty on expert (with the High level enemies mod) and I like a challenge but getting severely outdamaged in close combat is getting on my nerves.

I play a spellsword or battlemage however you want to call it. I use heavy armor, 2 handed weapons, conjuration (atronachs) and destruction. I have a mod for keybindings so I have quick access to stoneflesh which I like to keep up in combat, and for closing in on mages I use wards.

Im level 30 and I just cant get too close to enemies. I need a frost atronach or poor serana to tank enemies for me because they just 2 shot me. Does someone have any tips for me how to deal with this?

Lower the Difficulty a bit. Or play Smart, Use Cover. Run and Heal behind trees/rocks Play Smart, Play to Survive, Play to win.

not all of skyrim is leveled.
some areas have monsters that are always a minimum of a certain level.

maybe its the game telling you to level up and come back later.

What heavy armour perks do you have what's your armour stats and do you use block ?.

So let me get this straight. You set the game to a hard setting and downloaded a mod to make the game harder and now you're asking why the game is so hard?

Basically he is, Yes.