Hi I have a 15 year old son that has a lump in his armpit could this be lymphoma?

Hi I have a 15 year old son that has a lump in his armpit. He discovers it 3-4 weeks ago. I took him to the emergency room and they did an ultrasound and found 7 enlarged lymph nodes. He was prescribed antibiotics and finished them. The one lump is still there. He has ckd stage 3 and has one kidney. My question is could this be lymphoma?