Please help! Going out my mind x

Hi, I got diagnosed with lobular cancer in December 2021, stage 2 invasive. Cancer was HER negative and The cancer was 2.4cm. I had three lymph nodes removed in my armpit one being the sentinel lymph node. These came back clear with no cancer present. I then had radiotherapy 12 weeks after my operation (lumpectomy) late due to Covid. I have developed a hard lump under my arm on the side my breast cancer was present. The lump hurts when I touch it and then my full arm has a weird sensation down it. I Went for my yearly mammogram which looked normal however they sent me for a biopsy on the armpit lymph node and ultrasound. The ultra sound department said they score the lymph node U3? What does this mean please? I have to wait 3 weeks for the results and I’m going out of my mind with worry incase it is secondary cancer.

thanks so much x

thanks x