I have been going out with my boyfreind for about 3 months total, and he doesn't really like to show emotion at all. He kind of smirks sometimes but that's it pretty much, he has built a wall around his emotions because I think someone hurt him in the past but I'm not quite sure at all. I have tried getting him to smile but he always drops the subject and starts talking about something else. He loves me very much and I feel the same way for him. And that's why I want to help him overcome this.

All I can say is give him time and don't try to force him.
If you are willing to put in the time and effort into earning his trust, then I admire you greatly.
It is hard for someone to trust another after they have been burned, I know this from experience--I too have been hurt by someone I once trusted.
But once you find someone who is willing to work through it all and those defensive walls come down, it is such a great feeling of relief.