I'm sorry you are having a hard time, being and pain and overwhelmed. I think it's not helpful to be told that you are 20, so you should just be able to snap out of it. It's never easy, regardeless the age. Our issues always feel heavy to us when we are in pain.
So, it's understandable you feel the way you do.

Also, yeah, your father might have the right to demand things because you are living there, in the same time an understanding father would support their child when going through tough times. Then, he is most probably still suffering after the loss. In these situations pain can make people do and say things they wouldn't normally do. But I don't know the exact situation.

Also, you might be convinced now that what you want to do is impossble and it might even very much seem so, but maybe there are things you could do to mve towards it in the future or something similar? Not sure, maybe not, just asking.

Is it possible for you to get some help, talk to a therapist for example? It is possible that you are depressed to the extent you cannot work right now. Hope you can talk to someone to help you through this

Meanwhile, feel free to share your thoughts here.