I keep thinking I have a disease?

I hate to put another idea in your head but there is actually something called hypochondria. That is basically when someone has a strong fear that they are sick with some kind of illness and make up all these symptoms in their head that don't actually exist. Depending on the duration of time that you have had this, this could be what is going on. What you need to remember is that this is not some kind of disease that needs treatment. You don't have a problem that needs any kind of medication. I would talk to your parents about the situation with you dad because it looks like it had a greater effect on you than you know. You were probably scared for him and because of that are now scared about yourself too that you would have to go through something serious too. I wouldn't tell you to never see a physician if you really think you have something but make sure you are talking to your parents and let them know everything going on with you. Remember that these kinds of diseases like leukemia can only be diagnosed through a blood test as their are no physical symptoms for it. What I would say is try not to think about being sick too much. Take your mind off of your health and you should be fine.