Hi. Since I turned 40 in July, I've noticed a hard round lump on my left breast that is more prominent when I am lying down and when i raise my arm. It is very movable and I can see it move under the skin when i move it. It seems to be linked to my menstrual cycle as I'm fairly sure it does shrink after my period but am still a bit worried. Any help and reassurance would be appreciated. I will wait until after my period and if it hasn't changed I will go to the doctor.