Pain under armpit

I feel under my arms and breasts nearly every day as im so paranoid something is wrong for a while under my left armpit more on top of my breast there’s been like a constant pain I’ve only just realised this come and goes I’m not sure if this is because of my period or where I keep feeling under my arm but I’m scared to the doctors in Case there is something wrong but at the same time I don’t want to leave it