I have been playing at Level 48 forever, it seems. The blue bar is full, have completed several quests at this stage (full blue bar), but I don't advance to L 49. Suggestions?

Read a skill book, train, or reload a save. There.

Thanks. Will try the skill book and/or train. Have reloaded many saves.

You don't get experience points from quests and stuff, you just get better at things by hitting them. 48-50 is usually the highest you'll go with one archetype.

Stupid question, but what do you mean by archetype? What do I need to do to get higher?

Archetype as in the kind of character you play, since Skyrim doesn't really have "classes" per se. For example, if you're a pure warrior, start doing some magic stuff, or if your smithing isn't high, level it up., etc.

Generally when your skill that you use for killing hits 100 your leveling slows down significally.

Basically, what IKillPeople is trying to say is, you don't level up by doing quests, you have to level up a skill, make sure that the skills you are using are not level 100, if they are, you'll need to adopt a new skill or two to level up.

Spot on, mate.

Exactly. Odds are that you main armour skill and main attack skill are either at 100 or pretty close. So use a different type of weapon. Or use the same weapon, but a different type of armour. Cast a lot more spells. But try to avoid doing all these at once because doing so will seriously weaken your character.