Yes, it basically means "well" .. like in: "Well, I think I'm fine" --> "Ами, мисля, че съм добре", but it can also be used as "Really?!?" --> "Ами?!?" [you know .. when you're so surprised you can't believe your ears :P ] . However, it's only used in colloquial speech.
*If anyone knows any other meanings of "Aми", please share them, because that's all I can think of right now :]