Do I have breast cancer?

My breasts are sore and I'm not certain why. Two weeks ago I've been diagnosed with type one diabetes, so I have to exercise every day which isn't something I'm used to. Could my breasts just be sore from the new exercise along with stress (and that I need a bigger bra size)? I don't see any lumps but my breasts feel a little tight, my nipples are normal looking, and my skin texture is normal except for a few red scratch looking marks which somehow got there. It hurts to lay on my side but it doesn't hurt when I breathe or walk, but sometimes feels uncomfortable. Does this sound like breast cancer, or just soreness?