Any tips or explanations? In a sense, I'm not completely complaining... it is good to have to work for things...

So I'm a dark elf. Thieving, using destruction magic, one-handed and light armor. I've got a decent elven armor w/ +40 health, and decently stocked and decent weapons. Was using sword, but now switched to war axe w/ perks helping it. sneak is good, bow always when I can to start combat.

Now, up to level 15 I mostly almost never had trouble except for boss-like fights or giants or mammoths...
Suddenly since level 15, there are combats I get into were I get mauled in like 3-4 hits. As if my armor is crap or my health is weak.

Every level I'm almost always pumping up health. (should I do it to stamina? does stamina do anything other than stamina bar and carry weight?)... but it seems not to help much.

I was walking north from the greybeards' mountain to the quest, and i ran into a fort. some guys outside, all wearing steel, not too much trouble when i took care of them playing smart and sneaky.

Then I go inside, and in the prison tower I got DENIED by their "chief". The amount of potions/spells/tricks I had to do was insane. All of a sudden I'm starting to lose a lot of potions I had almost never needed before...

Now I'm approaching level 19, and in a temple with orcs and priests awakening from some deep slumber and again, at times they die in like two arrows, but at times one of the orcs will just maul me in about 3 swings.


Is this all normal? (again, I somewhat appreciate it... gives a sense of worry to things)... is it just the way skyrim is setup, such that eventually you need to start buffing up prior to combat areas (and not wait until combat)?

Or should I start worrying a bit, and realize that maybe I'm falling behind somewhere -- armors? (doesnt look like it).

Bosses are usually tougher. It is normal. There are the normal foot soldiers and later in a dungeon you encounter some boss which takes a bit more to kill. At least this is my expereince.

However, let me clarify I'm not talking about "bosses". Basically the last few days of play, level 16, 17, 18.... just about every encounter is real trouble, perhaps 2 reloads on average... im starting to quicksave more, and I don't like doing that...

This is normal. Your character is going through puberty. Keep grinding through the ranks and you'll find enemies to be progressively and progressively easier provided that you continue to update your weapons, armor, and related perks and skills.

Seeing the same thing. I am now level-18, playing on expert. I killed the 3 sons for the Amulet quest. That was doable, but not trivial. Now I tried to kill a Vampire called Movarth. No chance. Then I decided to go do something else. Went to Wolfskull Cave to clear it out. Soon I had to jump down a hole, and there were a few mobs waiting below. Because you aggro them all at once, I could only stand there and take a beating. I'll try again tonight (it just occurred to me that I can just keep throwing fireballs, even though I'm not a mage. They can't get back at me anyway). But things suddenly seemed harder in dungeons.

Haven't had any gear upgrades since lvl12 or so. And I'm hesitating to go do blacksmithing to get me better gear. If I depend on quest rewards and loot from dungeons, that path seems very random and unreliable. I could just as well go another 5-10 levels without any (relevant) gear upgrades ?

I guess the best strategy would be to try out different quests and dungeons, and see which ones are doable ? Seems time-consuming if that is the case.

your last point about 'try something else', in fact, is a good thing to think about. See, I happen to be one of the gamers that believe that indeed, scaled-difficulty takes away the fun of a game. In practice, I do long for a game that has a place that once you go to it you get your bum wiped, and then realize "oh my, I need to come back later". Of course I'd like to know that behind those difficult encounters lies an amazing reward... which I have yet to find.