I don't care that my grandmother died yesterday
Do you really mean that?
I don't care about her anymore.
I'm sure you don't actually feel that way, she was family!  You should let your guard down a bit.  Grieving is okay!
I don't feel bad I just don't care.
I think you just need to get in touch with your feelings a bit more.  Grieving the loss of a loved one is a natural part of life.  Forcing yourself to feel nothing is unhealthy.