I Had Triple Positive Stage 2a Breast Cancer In 2014.

I had triple positive stage 2a breast cancer in 2014. I had a double mastectomy with no lymph node involvement. So now, of course, everything that happens makes me worry. Recently, I began walking, running and doing abdominal exercising on a hard floor. A few days ago, I started noticing pain in my mid back, just to the right of my spine. There is a knot there, like a muscle strain. It is super sore to the touch and if I lean against something. There is a little soreness with movement. Should I be worried?