Hi, I Had A Mammogram Recently And The Breasts Were

Hi, I had a mammogram recently and the breasts were all clear but the scan showed a slight thickening of lymph gland right side. There is no swelling etc and doctor could not feel anything. I was advised it could be because I had torn bicep injury which is still healing. The Dr said to have anther scan in three months. 7 years ago I had a lumpectomy on the left breast and some lymph glands tested which were clear. I had radiation only and clear every since. Please can you comment as I am worried. I don't really understand what thickening means. Thanks