You are FINE! You have a healthy immune system battling continually against invading germs. As one just finishing a mastectomy I also am very sensitive regarding changes I see and feel in my body. We will see fluctuations but prayerfully will stay healthy.
You wouldn't be able to "feel" a lymph node as they are quite small. Mammary nodes are not really an unusual finding but I'm sure if this node raises suspicion you were advised to have some additional testing. If you have concerns about this you should discuss this with your Oncologist. Regards ....