Is it the fat under the armpit near the accessory breast?

I'm not sure if my accessory breasts have gotten bigger, if I've gained weight, or if it's both, but that particular area has gotten larger. It's really uncomfortable in that spot when I wear T-shirts, especially the smaller ones. I'm wondering if it will naturally disappear if I lose weight, or if I need a procedure, and if so, what kind of procedure would be best.