Lump in armpit

This might be stupid to post about, but I have a lump in my left armpit that I noticed for the first time late last night. It is painful to touch and I feel like it has gotten bigger since last night. I'm 36 weeks along and I haven't had any leaking or milk coming in, would this be something to do with milk production starting soon? My doctor's office is closed today but I'm planning to call tomorrow on my break at work to see what they say if it doesn't get better by then. Any insight would be very helpful, thank you!