Lump on underarm

I am currently 27+4 weeks pregnant and I have a small lump under the skin of my underarm maybe the size of a dime. I Can feel it all the time but it’s only slightly visible when I stretch my arm far back. It doesn’t hurt. I’ve read we have breast tissue in our underarms and it can be a duct which is common during pregnancy.

I have an ultrasound on Friday 1/26 and an OB appointment on Monday 1/29. Would you suggest I call my OB or just wait until 1/29… if I were to bring it up to the ultrasound tech , would they be able to look at that right there and then?

Thank you,