I was the same kind of person a few years ago, and I think I never really wanted to show any emotion , but I started faking emotion to get by, fake smiles, fake affirmations, and then over time people slowly started trusting me...

But the most surprising thing was, as they let their guard down, I began to realize I could lower my own, If you want to show your emotions, I suggest experience other people's emotions first, that will make you comfortable.

And most of all trust your instinct and take it easy, if you dont feel like showing emotion ,dont force your constipated soul, everybody has a different level of emotions within them, and they must flow, just try having light discussions with people and slowly but surely you will trust them, and gain your emotions.