I’m very sorry you are feeling so frightened and pessimistic. As painful as it is, it does make a kind of sense. People as young as yourself generally don’t think about death a great deal because they haven’t yet experienced the loss of someone close to them. (The exception, of course, is for people who live in a war zone or where there is an epidemic.) You, however, lost three people who were important to you in less than a year. That’s loss upon loss upon loss. When that kind of thing happens, it makes death and endings much more real.
Whether consciously or not, you are processing what it means to end. At the same time, it’s natural for someone your age to continue to grow and look to the future. Both are real and important issues. Yes, we are all dying from the moment we are born. But we also have a life to live. Reconciling those two things is something most people do much less consciously but everyone has to do it. Because of your losses, you are much more aware of the existential dilemma.
It’s likely that the people who love you don’t understand this. If you talked to them, they would probably encourage you to get past the losses and see the good in your life. That’s all true. But because you are someone who thinks and feels deeply, you also need to come to terms with the ephemeral quality of life. For that reason, I suggest you seek our a therapist or spiritual leader who is familiar with this issue and who can guide you to new understanding.
I wish you well,