I feel so embarrassed asking this, I have had a very sore pain in my left breast for a while now and I'm really worried there could be something wrong, my mum said its nothing but I'm not too sure I'm 15 years old. I haven't done anything straining or anything like that and I can't even sleep on that side of my bod. Is it normal?

This could be a growing pain. If you are really concerned, tell your mother this pain hasn't subsided and you want her to make you a doctor's appointment.