I've been taking some singing lessons lately and I really feel like the main error I have to absolutely correct is lack of emotions and expressiveness in my voice. My teacher some times tries to make me interpret the song, reciting it instead of singing to improve on that aspect but I'm not even close to satisfied with the results. Reciting it makes it even more evident my incapability of expressing emotions through my voice.
As a person, I'm a bit of an introvert, not like shy, but I don't talk a lot. I think the problem with expression is true for my voice generally, even when speaking. I use a "flat" tone and volume but I don't really know how to work on this. Note that this problem is only true for my voice. I've never had any problem in communicating emotions with my facial expressions and words.
Any suggestions, exercises or even an explanation on what kind of role all this has in singing?