Hi SROB1983, I am so sorry for your loss.
I am having a problem that is very similar to yours. I have had an unusual number of losses (family and pets). During the past 4 years I have become fairly obsessed with thoughts of loved ones and others, even strangers, dying. For example, I have five cats that I love every much. Every time I look at them I think about them getting sick and what it will be like when they are dying or dead, and when it will happen. I do this with people, too. It's like living death, not living life. Nothing has helped me, and I also wonder...is this OCD or PTSD? I do have moderate OCD, and I have been diagnosed with PTSD, but my question still remains. I am on several meds that help me, but nothing has stopped the death-thoughts and other "dark" thoughts.
I was on a long waiting list to see a therapist in my town and I finally have an appointment with her for Friday. When in therapy, I will be focusing on the very question you and I are both asking. My general belief is that what you're describing is a combination of PTSD and OCD.
By the way, Welcome to PC