Lots of medical tests -- and it's possible one of those tests may find something else accompanying the depression.

Jazper, if you feel in crisis, then perhaps you should listen to yourself and treat this as a crisis. Try to allow yourself the freedom to be in crisis and step out of routine to deal with what you are facing. Addressing issues now is preferable to confronting worse later.
I don't know. Maybe someone closer to you does or will know. You have repeatedly (I think) borne the privilege and burden of being with those who are passing from this world. Does that have something to do with your hurt?