My condolences on your loss. I don't know what your dad died of. But I can't imagine it was your fault. But coping with the loss of a parent can be difficult especially for someone as young as yourself. Hopefully posting, here on PC, can be of some help. But, really, the thing to do I believe is to find someone in real life with whom you can talk about your struggles.

Someone you might talk to could perhaps be a school counselor, a trusted teacher, a relative such as a grandparent or an aunt or uncle if you are in touch with any of those people, or a professional mental health therapist if arrangements could be made for you to see one. It's continuing to hold inside all of the sadness of what you have experienced that is going to continue to cause you to suffer. Please take care.