Help? Why don't I feel or am unable to express certain emotions?

My childhood past was really rough... and as grew i noticed that I don't feel love and I cant express sadness. The emotions I do feel are things like frustration, happiness, confusion and anger, but I can't tell anyone I love them, not my family or any boy that has expressed his feelings to me. Usually i just feel, well blank when it comes to love. When it comes to sadness I cannot cry, nowadays I cry about once every 6 months over small things that shouldn't matter, and I only cry for a short time even though I often feel compion and empathy for sad things that happen to people. Also when someone dies I don't really feel the loss I just feel a sense of emptiness and a twinge of compion for their family. However for every other emotion I have no problem which is what confuses me.