M.C.
I actually had a very similar situation but they were not nearly as alarmed or thurough with me as they were with you. I had a lymph node in the side of my breast that swelled up during pregnancy and then became larger and worse after the baby was born and thru nursing. I stopped nursing and the lymph node stayed. Because of my family history I was sent for an ultrasound and then also a mam. They saw the lymph node was enlarged but couldn't tell why. They did some blood tests and found nothing. I did not have a biopsy or chest xray. I was told that with nursing sometimes the lymph nodes will become enlarged to protect the breasts from infection. I guess that's what the lymph nodes do in general but because it's such a close proximity to one another that the nodes can really become very large. It's a protection mechanism for our body and that's what they do. Likely your immue is down because of the current pregnancy and you're still BF so it seems to me that your body is just fighting something off so your milk ducts don't become infected/clogged. They took my case very serious because my mother had just passed from breast cancer but they told me that typically they would not have even looked into it, I guess this is common for some people. I'm happy they were so thurough with you but I thought that wasn't common. But who knows, it's a case-to-case situation. Anyhow, maybe ramp up on your vitamins and do a lot of massage in that area to help drain it. I'm not a doctor and I'm sorry you're in this situation but they did everything they can do now and it didn't show anything. I sincerely don't feel surgery during pregnancy for this would be worth it. Just give it some time. I had mine swollen for a total of probably close to 10 months before it entirely went away.