Oh Glory, I am sooooo sorry. I have been there. Not only for breast cancer, but earlier this year when they found a nearly 5 cm lump in my stomach ( after bleeding problems from my meds ).
It sucks. It comes in waves. You are ok then it suddenly hits in a wave of anxiety.
A couple of things helped me. I had a plan. I knew where I would go if it was positive. The breast lump was. I had it all worked out in my head. That gave me a sense of control. I also reminded myself, that I had access to EVERYTHING that I needed to handle it. We have so much in this country. So I would often tell myself, "Thank God that this is happening here, in the US. "
The fact that it took three weeks to get you an appointment is actually a good sign. It means that the medical personnel don't see it as "urgent'. After they ultra sounded my lump and felt it by hand, I had a biopsy in 3 days despite the fact that they couldn't see it on a mammogram. But I also got a ton of comfort that it was under 5 cm.
Do whatever you can to distract yourself. Turn up music and dance, watch inspirational Ted talk videos or silly videos or whatever videos. And please keep reminding yourself that you CAN and will face whatever "it" is and that you are so lucky that they caught it on a mammogram because now you will handle it.
GOOD LUCK !!!
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