breast cancer????

so I am 6 weeks post partum and 19 years old I have recently developed a lump under my armpit that hurts bad and it feel like its spreading down my arm and under my right breast I don't want to jump to conclusions or anything but I'm so scared it could be breast cancer I am not the type of person to complain when I feel something is medically wrong with me it makes me feel like it looks like I'm just one of those ppl who seek attention from it so usually I don't tell anyone but I am terrified cancer runs in my family bad and I'm so scared I'm only 19 and I'm waiting for my doctors office to open and its stressing me out bad I just don't know what to do or think someone pls pls caom me down or something