When you lose someone so close to you, like a parent, it’s absolutely normal to feel that way, especially when that happens in a young age such as yours. I too, when I lost my father 11 years ago had several odd thoughts that didn’t represent me, but in my case it wasn’t so much a concern about my health, as that I need to hurry and do certain things before I die. These thoughts and fears pass with time.
I’m afraid that since you can’t communicate clearly with entities and the dead, there’s no much you could do to get the answers you seek, but you can always petition an entity to escort his soul to the other side.
A way you can do that is with this tutorial for petition spells from DK.
Another thing you can do, is to honour your father according to your tradition, whatever that might be. For example, for my tradition (that doesn’t have anything to do with the religion my father followed) is the choe, aka libations for the dead.
Take your time to mourn and come in terms with the loss. Remember that the end goal is to leave the pain and fear behind and not linger over it. Always live in the here and now and appreciate what you have and what you can experience now.