Lump in armpit 😥

I’m 19 weeks pregnant and I noticed a large soft lump under one of my armpits and it’s making me worried!

My next appointment is in 2 weeks so I’ll ask about it then, but has anyone had this and know what it could be? 😥

It’s pretty large, soft to the touch, and maybe a little hard towards the bottom. But the large part of it is soft.

Edit:

You can really only see the lump when my arm is down:

Right side for comparison with no lump:

You can’t see the lump when my arm is straight up so I didn’t include a picture like that, but I can still feel it when my arm is up.