Helppppp this is literally life or death!?!

Is your Dad a doctor? Even they can't really predict how long you will live.
You, however, have a choice in the matter - that is to choose to live your best no matter what doomsayers might say to you. Your life is worth living so put all the best you can into you for yourself and others (I found that helping others can help me too).
There's a good book entitled, "You can't afford the luxury of a negative thought" by Peter McWilliams - you can look for it at your public library or used bookstore. It's fun to read and there's a lot of truth in it too.
I wish you good health and happiness, I think your dad's rude, but he might be trying to get you to fight for your life.

Life 101 books, personal experience, my humble opinion.

ok well i don't know anything about this disease but firstly if it's just your dad teasing you a lot about it, then it's probably not going to happen. You need to talk to him it's difficult i know but if he has a shred of respect for you (which he should, he is your dad) then he should listen. Tell him the jokes are getting old and you really are worried, so you would like his support and if he can't give it to you you'll move to a more positive environment. Live to the full every day is a precious thing- lol can't believe i'm saying that i'm practically in counselling but good luck to you

ok first, sit down in a chair, feet flat on the ground. put your hands on your lap and close your eyes. breathe in and imagine a feather floating up, and exhale and imagine the feather slowly falling down. keep doing this for a couple minutes.
Next, I'm sure your dad loves you. You need him and he needs you so you two have to try to bond. However it isn't right for him to say that you are going to pass at nineteen, because nobody knows when anyone is going to die except for God.
you're very brave and God bless you =)