I am sorry you are suffering so much, mentally and physically. It sounds like you are not getting the support you need for your mental health issues. Do you have a good relationship with your primary care physician and have you tried different medications?
Does your cancer centre have a support group that could help? The physical effects of the treatment are difficult enough if you are emotionally in good shape but I am sure magnified by the anger, depression and anxiety. I hope you will be able to find some help soon, please don't give up.

Caregiver to husband Dx. Stage 4 SCC of gingiva with 3 nodes pos. Partial mandiblectomy with bone graft from iliac crest Dec. 2006. IMRT x30, Cisplatin x3. Completed Tx. March 15, 2007. Osteonecrosis & removal of graft & plate Oct. 2007. Recurrence of SCC Dec. 2007. Deceased Jan. 17, 2008.