Dull ache in right armpit

[Pickles31]

I’m 40 weeks 2 days today with no sign of baby yet and woke up in the
Night with a dull ache in my right armpit like I’ve pulled a muscle, has anyone else experienced this and could it be something to do with my milk ? It only seems to be the right side

Not really sure but I've had it a few times in the last few weeks- left side only and it disappears after a day or so. I assumed milk production as couldn't get any answers anywhere. I'm 39+5 for reference x