Why do I lack care?

So I noticed thaat I often seem to lack care for others. If I think about what I feel for my friends and family my mind goes blank, I simply don't know what I think. If I think about it, it is so easy for me to find anger towards those people for various reasons and sometimes stupid. I don't know how I feel about my friends. I once had a big fight with one of my friends and I can still feel so angry about it even after we talk it out. I have good friends but I don't feel it. I don't feel intense care for them or for anyone. I see people who love others so much , but I just don't and that makes me feel sad sometimes. I wish I just really cared for them. But I don't care so much as others. Why does this make me feel sad? Is this normal? I just don't get it. I makes me think I'm selfish and a bad person