The ears are still "setting up" (my terminology, not the correct verbage, I'm sure) at that age and he might be starting teething as well. During teething, it's not unusual for the ears to flop around a little. I would massage the ears for a few days and see if it stands up straight again. I used to start at the base of the ear and massage up to the tip. Very relaxing for everyone involved, especially Levi. LOL! It isn't anything I would be overly concerned about at this time.
My german shepherd went through this phase with her ears as a puppy. Really freaked me out at first, but it seems to be due to uneven growth (inside of ear growning faster than back side) and will be just fine on it's own. :-)