Terrified I have Secondary Breast Cancer

After 15 years when I had heavy node involvement the breast cancer has retuned in the other breast.
I have 8 visits to the breast clinic whee they said it was just pre cancerous cells that they would remove. I finally had surgery where they removed a 45mm area and a 3mm cancer was found. Although they got clear margins they need to take a little more out and check my lymph nodes.
I have had a backache since this all started and am having an MRI on Sunday to check its not spread. I’m feeling pretty shellshocked at the moment and just wanted to chat to someone who may have gone through this. Thank you.