Should I be worried

I had breast cancer 13 years ago. 

All was dealt with was aggressive  

I choose not to take tamoxifen after it made me feel so crap all the time. 

At the weekend I had a sharp pain under my bra strap in the centre of my back. It was excruciating. 

It is still really sore now. 

I also have a pain in my hip joint and down right leg. 

I am scared this is lung cancer or some sort of spread. 

But feel stupid calling the GP. 

Any thoughts.