Any thoughts?

Hi, I posted here a while back, so briefly this is my story! I had a melanoma in-situ 10 years ago, in January this year I got out the shower & noticed an odd pink patch of skin with very enlarged pores on my left breast, it has faded somewhat but I know it's there & Dr Google (which I know is bad) came up with IBC. So gp referred me to breast clinic, mammogram & ultrasound clear, I saw a dermatologist as well who didn't seem concerned. That was all back in Feb/March time. My anxiety levels went down although I do keep an eye on it. However 2 weeks ago I felt a hard marble sized lump near my armpit. I do not have one the other side & I don't feel poorly, I feel it more prominent when sat up & I have done my best to not prod at it. My question is could it be just a lymph node? I have one in my neck that never goes down but that one is more oval & squidgy!
Any thoughts are appreciated, I suspect I'm paranoid & it's just coincidence it's the left side.