more thanks

I am due to have a mastectomy next Friday and am so scared of the whole procedure and not waking up from the anaesthetic. I never imagined i would have breast cancer, have breast fed three children, exercised every day and eaten healthy. I am worried about the sentinel node thing, as my pathology from core biopsy says that there is no lymphovascular involvement, but the breast surgeon says that they still have to look at the nodes. It's Stage 2 Grade 2 and I am terrified that it has spread. The ultrasound said that my lymph nodes are not involved, then why and what is the significance of the sentinel node and if it's involved does it mean that I have secondary cancer somewhere as well. Why do I have to wait for two weeks after my mastectomy before I can start treatment? It's invasive lobular with high oestrogen and progesterone levels. Why can't I begin treatment earlier or is this normal length of time?