Breast Cancer

I went for my yearly checkup today as I have now been 8 years clear from breast cancer. I had my breast removed with a node clearance followed by chemo and radiotherapy then reconstruction after. This was followed by 5 years of tamoxifen then letrozole of which I managed to deal with . I was discharged from being under the hospital today and am now being placed on the 3 yearly mammograms as of next year. I only have a few more years on letrozole then they will be coming to an end of which I am so worried in case it returns. Does anyone know how long it stays in your body for afterwards?? And is there anything you can do in between mammograms other than checking yourself?
Thanks in advance