Hello, I ve had left sided chest pain for a long time. It affects the area under the breast, the breast as a whole, under my left armpit, and can affect my back as well (directly behind the breast). There s burning, piercing pain right through to the nipple. Pain can get worse at night when lying down. I was rear-ended in an accident 5 years ago. I had a mammogram and ultrasound and both were negative. I also have mild chronic gastritis and herniated discs in my neck. Thank you, Lisa