Just started - level 10, but stamina runs out instantly. My character can't get good sleep due to being a werewolf. Any way I can correct other than using up magic potions?

I think you're confused. Stamina is unaffected by resting and by Magic Potions.

What affects it then?

Stamina potions?

If you think you need more Stamina, just put points into it on level up, but you'll never really have enough. I have 250 at the moment and I still run out of it during combat almost every time. But then again, that's what it's for.

Wearing armor(heavy or light) makes sprinting harder. Also, you may have a disease that lowers your stamina.

Get some extra stamina when you level up, enchant gear with stamina, enchant gear with stamina regeneration, use stamina potions.

Don't sprint everywhere and not every attack needs to be a power attack.

Awesome - thanks

Keep a warm bowl of Venison or Beef Stew or Vegetable Soup in your belleh! You'll not be able to sprint, but you'll always have the energy to bash or power attack.

Or carry several dozen bottles of Mead with you, and every time you want to power attack, take a swing.

That would be pretty awesome.

Awesome mental image there

Get items that help your stamina regen. I got my enchanting up to 100 and now I almost never have to worry about stamina. Like a lot of other things in Skyrim, you'll never seem to have enough until one day you hit a sweet spot and then suddenly you never have to really worry about it again. Kind of like gold, there's not enough uses for gold at high levels. You scrounge and scrounge at lower levels, and then suddenly you're married, you have several houses, and you can craft/enchant your own gear, and you just don't even know what to do with what you have.