Hi Barks34,
I just want add that I get it. I suffer from depression/anxiety and take medication (just 20mg per day) which takes the edge off it. I am in the middle of swapping to one that will not mess with Tamoxifen. Traumatic life events can "trigger" depression. In the past, when in crisis (before cancer), I have had cognitive behaviour therapy. My GP made a Mental Health Care Plan
https://www.healthdirect.gov.au/mental-health-care-plan which means you get a Medicare rebate for part of the cost. Given your location, maybe you could access a therapist online? Your GP needs to address this ASAP!