FWIW, I'm having the same problem with an up-close-and-personal guy. I'm on expert and it's still pretty easy -- although I did run into a couple of tougher battles recently.
Are you still playing on expert or did you bump it up to master? In fairness to Bethesda, I think they expect you to be kind of "over it" by level 40-50. And it's not like ~120 hours is unreasonable to expect a character to have done everything that makes sense (i.e. main quest + a couple of guilds). I suspect starting a new game on a higher difficulty from the outset will add to the challenge significantly.
I don't really enjoy doing it all in one playthrough anyway, so I guess it's good that the way things are set up make me want to start again with a new character. I'd feel stupid blasting my way through the companion quests (aka fighter's guild) with a lv42 mage. And let's face it... everybody's complaint about Oblivion was that you never felt like a world-beating badass no matter how high your level got, so we got what we asked for
