Doctors dont pay too much attention to lumps during pregnancy, as our bodies are preparing for breastfeeding.
I found a lump under my left areola around 29 weeks. At same time gynae was on vacation and I only saw him again last week at 33weeks. I was very anxious for these 4 weeks.
Told him about it at the last scan, he did an examination but does not seem concerned as its probably a blocked milk duct. I'm sure he'll be keeping an eye on it.
I'm not so sure about those under your arm, but try not stress too much. And tell your gynae about it next time you see him, or if it will make you feel better, give him a call rather.