Ooh, so yesterday I came up with an alternative internal vs. external conflict for one of my characters. It would fit very well, maybe better than my original thought.
By now, we should know our characters, so lets move on to how those characters interact. This is the place where all those internal and external conflicts will start to collide. (Internal and external conflicts should exist for all our characters, even the antagonist.) Some of your characters might already know one another. Some characters may only come in as the story progresses. Do your antagonist and protagonist already know one another? If not, why are they in conflict?
What allies or friends does your protagonist have? Allies seems to imply people picked up along the way in a quest, friends implies previous relationships, the support network you call on when in stress. That could make a big difference for your character.