grieving sucks

My mom had breast cancer for twenty years, and last year it became metastatic, meaning it spread everywhere: her liver, brain, bones, etc. I spent this entire summer taking care of her and helping her with her daily activities like showering, bathroom, and getting dressed. She died a little over a month ago, and I cannot stop crying myself to sleep. Talking to friends does not usually help, because they dont know what to say to me. I write in a scrapbook type journal and that helps for about 20 minutes. Im a nursing student, so cancers come up in class quite a bit and i find myself thinking about her and what happened and recapping the last days with her over and over in my head and its constantly upsetting. Im sick of being depressed.