Lump in armpit @ 16 weeks

Sorry this is kind of long- I am hoping someone else has had a similar experience and can give me some insight... yesterday I had my 16 week OB appt, where I had to see a midwife as my dr. was out of office. I mentioned a lump/bumpy area in my left armpit. I had something very similar on the same side that I noticed at the end of of my last pregnancy and my dr was confident it was accessory breast tissue. After pregnancy and breastfeeding I never really noticed it again. This time the midwife ordered an ultrasound as she said she could not definitely say it was breast tissue since it was a little higher up than she normally sees. I am freaking out. I had a stage 1 melanoma removed from my stomach in March 2019 and am so afraid it is something related to that. My husband said it seems very similar to what I had with my last pregnancy but I can’t stop freaking out. They couldn’t schedule the ultrasound until Jan 27 so now I will have to wait a month 😕. Has anyone experienced anything similar? Does it seem weird I am experiencing this so early in my pregnancy? Any insight is greatly appreciated