Small lump under arm

I found a small pea size soft lump under my right arm. This is not in my breast tissue. this is right under my arm where the hair grows. to compare, I checked under the left arm, there is other lump but almost unoticable.
I am pregnant.
now I remember I have it few months unchanged, but didn't bother to think about it.

shall I be concerned? (cancer or what?)