Skyrim is supposed level you for every 10 skill increases, I thought, but sometimes, when I get a skill increase, I get 2/10th of the way toward a level rather than 1/10th. As a result I'm leveling faster than I should (bad thing, because I have fewer skills for tougher mobs).

Tested it also using "player.incpcs " using new Nord character:
it takes 6x"player.incpcs heavyarmor" or 8x"player.incpcs illusion" to level, rather than needed 10 of either to level.

Can you help? Is there a console command that controls this? Is this supposed to happen?

... ruined my game!

That's the issue... it's not every 10 skills. It's variable - each character level takes more "experience" to go up; and the higher a skill is, the more "xp" each point gives.

(So, when you're level 20 - a skill going from 10 to 11 will only give you a small % of a level, while a skill going from 80 to 81 will give a lot.)

Hold on: are you saying,e.g., that I may receive a lvl per 5 skills early on but a lvl per, say, 20 skills later on.

Does the balance work as intended? (I'm acquiring far fewer skills as mobs get tougher.)

Related question: If I have a build that maxes, say, 5 skills to 100 which level should I expect to be then? (I would have suspected ~40 = 5x(80/10); assuming an average of 80 increase per skill?)

Yes, this is more or less the plan. Look at it another way: about 1500 skill increases gets you to level 81, about 750 get you to level 50. As you get to a higher level it takes more experience to gain a level but the higher the skill the more it counts at any particular level. So, going from 50 to 51 counts more than going from 15 to 16 but both count less at high levels.
I just did a character that focused on Illusion, for example, and going to 90 Illusion got me to level 16 with only 90 total skill increases where normally I would expect 90 increases (at a more balanced mix) would only get me to about level 12.

don't take the mage warrior or thief stones and avoid the lover stone as well (or was it the lady)

anyways anything that boosts skill up is a no no AND go easy on crafting skills

It's the new leveling system. At first, you'll level very fast with EVERY skill so low, but as your certain skills get higher with more use, the game will level you hardly any if you raise an unused skill from 17->18 but much more if you raise your best skill from 85->86.

It's the supplement for a class system where you start out with a blank slate and the game discovers what your class is 10+ hours in.

http://www.uesp.net/wiki/Skyrim:Leveling

The formula for character leveling is as follows:
Character XP gained = Skill level acquired
Example: Training alchemy from 20 to 21 gives 21 Character XP points
XP required to level up your character = Current level * 25 + 75
Example: 100 XP is required to advance from level 1 to level 2, and 1300 XP is required to advance from level 49 to 50. This is consistent across all levels. (70→71 follows the same formula as 3→4)