Hi skyelillie,

Sorry to find you on here and that you're so worried and scared.  Fear and anxiety can take you to all sorts of bad places and you will only make yourself feel worse so try, if you can to take hold of yourself.  Breast lumps are very common.  I'm a similar age to you and was plagued by breast cysts since my late 40's.  They were all benign but troublesome and they caused me a lot of worry.  
Most breast lumps are benign and only about 1 in 8 referrals  will result in a cancer diagnosis (this is what my GP told me at the time).  Unfortunately these things need to get checked out at the breast clinic and you will have a mammogram/ultrasound and maybe a biopsy.  Don't panic if they do a biopsy.  These are done just as much to rule out cancer, not just to confirm it.  Just being there and having to go through the process is pretty grim and the wait for results is tough but it helps to distract yourself and try to keep some perspective.

Earlier this year I was diagnosed with a small early breast cancer which was found when I was getting another cyst checked (cyst was fine)!  I'm pretty grateful for those cysts actually as it meant everything was found and treated promptly.  The thing is you won't know for sure until you get it checked.  You have to go through this unfortunately but when you skip out of that clinic with the all clear it's a fantastic feeling.  Likewise, if anything is found you will be well looked after and supported through the process.  In the unlikely event that a breast cancer is found there is so much now that can be done.

Dont forget stress can cause all sorts of symptoms and your sore sternum may be just inflamed cartilage in that area which is quite common.

Good luck with everything.  There's every chance you'll be fine.

Mary