Breast clinic referral age 26

Hello, I am new to here but wanted to say hello and for some advice. 

I have had an armpit / breast pain since around September. All has been on my right side. I went to the doctor in October, examined and chatted. My doctor told me to come back if nothing had got better. 

Fast forward to middle of December and the pain is still there, in my armpit, breast and now below my collar bone. A niggly dull pain that won't go away. The doctor examined me again and noted that my right breast may look a little fuller since last time. So she referred me to a breast clinic for an ultrasound. Since my doctors visit, I now have a little back pain at my shoulder.

I am getting a little worried waiting for this letter, waiting for the mail to arrive each day. How long is the wait usually for the letter? I live in Scotland. 

And how is best not to worry about it all? The more I try to not think about it, it is always on my mind. 

Many thanks